diff --git a/CHANGELOG.md b/CHANGELOG.md
index a5e4e5b9..f4d98d94 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -35,7 +35,8 @@ and this project adheres to [Semantic Versioning](https://semver.org).
 
 - Improve Coverage for ODS Reader [#1545](https://github.com/phpoffice/phpspreadsheet/pull/1545)
 - Named formula implementation, and improved handling of Defined Names generally [#1535](https://github.com/PHPOffice/PhpSpreadsheet/pull/1535)
-  - fix resolution of relative named range values in the calculation engine; previously all named range values had been treated as absolute.
+- fix resolution of relative named range values in the calculation engine; previously all named range values had been treated as absolute.
+- Drop $this->spreadSheet null check from Xlsx Writer [#1646](https://github.com/phpoffice/phpspreadsheet/pull/1646)
 
 ### Deprecated
 
@@ -49,6 +50,10 @@ and this project adheres to [Semantic Versioning](https://semver.org).
 ### Fixed
 
 - PrintArea causes exception [#1544](https://github.com/phpoffice/phpspreadsheet/pull/1544) 
+- Calculation/DateTime Failure With PHP8 [#1661](https://github.com/phpoffice/phpspreadsheet/pull/1661)
+- Reader/Gnumeric Failure with PHP8 [#1662](https://github.com/phpoffice/phpspreadsheet/pull/1662)
+- ReverseSort bug, exposed but not caused by PHP8 [#1660](https://github.com/phpoffice/phpspreadsheet/pull/1660)
+- Bug setting Superscript/Subscript to false [#1567](https://github.com/phpoffice/phpspreadsheet/pull/1567)
 
 ## 1.14.1 - 2020-07-19
 
diff --git a/README.md b/README.md
index 893b3784..0fed4301 100644
--- a/README.md
+++ b/README.md
@@ -8,7 +8,8 @@
 [![License](https://poser.pugx.org/phpoffice/phpspreadsheet/license.png)](https://packagist.org/packages/phpoffice/phpspreadsheet)
 [![Join the chat at https://gitter.im/PHPOffice/PhpSpreadsheet](https://img.shields.io/badge/GITTER-join%20chat-green.svg)](https://gitter.im/PHPOffice/PhpSpreadsheet)
 
-PhpSpreadsheet is a library written in pure PHP and providing a set of classes that allow you to read from and to write to different spreadsheet file formats, like Excel and LibreOffice Calc.
+PhpSpreadsheet is a library written in pure PHP and offers a set of classes that
+allow you to read and write various spreadsheet file formats such as Excel and LibreOffice Calc.
 
 ## Documentation
 
diff --git a/docs/index.md b/docs/index.md
index c1a06459..b1207d53 100644
--- a/docs/index.md
+++ b/docs/index.md
@@ -2,9 +2,8 @@
 
 ![Logo](./assets/logo.svg)
 
-PhpSpreadsheet is a library written in pure PHP and providing a set of
-classes that allow you to read from and to write to different
-spreadsheet file formats, like Excel and LibreOffice Calc.
+PhpSpreadsheet is a library written in pure PHP and offers a set of classes that
+allow you to read and write various spreadsheet file formats such as Excel and LibreOffice Calc.
 
 ## File formats supported
 
diff --git a/src/PhpSpreadsheet/Reader/Gnumeric.php b/src/PhpSpreadsheet/Reader/Gnumeric.php
index f4a44895..dc921c1e 100644
--- a/src/PhpSpreadsheet/Reader/Gnumeric.php
+++ b/src/PhpSpreadsheet/Reader/Gnumeric.php
@@ -543,7 +543,8 @@ class Gnumeric extends BaseReader
 
                     $endColumn = ($styleAttributes['endCol'] > $maxCol) ? $maxCol : (int) $styleAttributes['endCol'];
                     $endColumn = Coordinate::stringFromColumnIndex($endColumn + 1);
-                    $endRow = 1 + (($styleAttributes['endRow'] > $maxRow) ? $maxRow : $styleAttributes['endRow']);
+
+                    $endRow = 1 + (($styleAttributes['endRow'] > $maxRow) ? $maxRow : (int) $styleAttributes['endRow']);
                     $cellRange = $startColumn . $startRow . ':' . $endColumn . $endRow;
 
                     $styleAttributes = $styleRegion->Style->attributes();
diff --git a/src/PhpSpreadsheet/ReferenceHelper.php b/src/PhpSpreadsheet/ReferenceHelper.php
index 9205b76e..13f7cf71 100644
--- a/src/PhpSpreadsheet/ReferenceHelper.php
+++ b/src/PhpSpreadsheet/ReferenceHelper.php
@@ -69,7 +69,7 @@ class ReferenceHelper
      */
     public static function columnReverseSort($a, $b)
     {
-        return 1 - strcasecmp(strlen($a) . $a, strlen($b) . $b);
+        return -strcasecmp(strlen($a) . $a, strlen($b) . $b);
     }
 
     /**
@@ -108,7 +108,7 @@ class ReferenceHelper
         [$bc, $br] = sscanf($b, '%[A-Z]%d');
 
         if ($ar === $br) {
-            return 1 - strcasecmp(strlen($ac) . $ac, strlen($bc) . $bc);
+            return -strcasecmp(strlen($ac) . $ac, strlen($bc) . $bc);
         }
 
         return ($ar < $br) ? 1 : -1;
diff --git a/src/PhpSpreadsheet/Style/Font.php b/src/PhpSpreadsheet/Style/Font.php
index eee7df04..a062a38f 100644
--- a/src/PhpSpreadsheet/Style/Font.php
+++ b/src/PhpSpreadsheet/Style/Font.php
@@ -357,21 +357,18 @@ class Font extends Supervisor
     /**
      * Set Superscript.
      *
-     * @param bool $pValue
-     *
      * @return $this
      */
-    public function setSuperscript($pValue)
+    public function setSuperscript(bool $pValue)
     {
-        if ($pValue == '') {
-            $pValue = false;
-        }
         if ($this->isSupervisor) {
             $styleArray = $this->getStyleArray(['superscript' => $pValue]);
             $this->getActiveSheet()->getStyle($this->getSelectedCells())->applyFromArray($styleArray);
         } else {
             $this->superscript = $pValue;
-            $this->subscript = !$pValue;
+            if ($this->superscript) {
+                $this->subscript = false;
+            }
         }
 
         return $this;
@@ -394,21 +391,18 @@ class Font extends Supervisor
     /**
      * Set Subscript.
      *
-     * @param bool $pValue
-     *
      * @return $this
      */
-    public function setSubscript($pValue)
+    public function setSubscript(bool $pValue)
     {
-        if ($pValue == '') {
-            $pValue = false;
-        }
         if ($this->isSupervisor) {
             $styleArray = $this->getStyleArray(['subscript' => $pValue]);
             $this->getActiveSheet()->getStyle($this->getSelectedCells())->applyFromArray($styleArray);
         } else {
             $this->subscript = $pValue;
-            $this->superscript = !$pValue;
+            if ($this->subscript) {
+                $this->superscript = false;
+            }
         }
 
         return $this;
diff --git a/src/PhpSpreadsheet/Writer/Xlsx.php b/src/PhpSpreadsheet/Writer/Xlsx.php
index 4cb10287..d71541c8 100644
--- a/src/PhpSpreadsheet/Writer/Xlsx.php
+++ b/src/PhpSpreadsheet/Writer/Xlsx.php
@@ -178,238 +178,234 @@ class Xlsx extends BaseWriter
      */
     public function save($pFilename): void
     {
-        if ($this->spreadSheet !== null) {
-            // garbage collect
-            $this->pathNames = [];
-            $this->spreadSheet->garbageCollect();
+        // garbage collect
+        $this->pathNames = [];
+        $this->spreadSheet->garbageCollect();
 
-            $this->openFileHandle($pFilename);
+        $this->openFileHandle($pFilename);
 
-            $saveDebugLog = Calculation::getInstance($this->spreadSheet)->getDebugLog()->getWriteDebugLog();
-            Calculation::getInstance($this->spreadSheet)->getDebugLog()->setWriteDebugLog(false);
-            $saveDateReturnType = Functions::getReturnDateType();
-            Functions::setReturnDateType(Functions::RETURNDATE_EXCEL);
+        $saveDebugLog = Calculation::getInstance($this->spreadSheet)->getDebugLog()->getWriteDebugLog();
+        Calculation::getInstance($this->spreadSheet)->getDebugLog()->setWriteDebugLog(false);
+        $saveDateReturnType = Functions::getReturnDateType();
+        Functions::setReturnDateType(Functions::RETURNDATE_EXCEL);
 
-            // Create string lookup table
-            $this->stringTable = [];
-            for ($i = 0; $i < $this->spreadSheet->getSheetCount(); ++$i) {
-                $this->stringTable = $this->getWriterPart('StringTable')->createStringTable($this->spreadSheet->getSheet($i), $this->stringTable);
-            }
-
-            // Create styles dictionaries
-            $this->styleHashTable->addFromSource($this->getWriterPart('Style')->allStyles($this->spreadSheet));
-            $this->stylesConditionalHashTable->addFromSource($this->getWriterPart('Style')->allConditionalStyles($this->spreadSheet));
-            $this->fillHashTable->addFromSource($this->getWriterPart('Style')->allFills($this->spreadSheet));
-            $this->fontHashTable->addFromSource($this->getWriterPart('Style')->allFonts($this->spreadSheet));
-            $this->bordersHashTable->addFromSource($this->getWriterPart('Style')->allBorders($this->spreadSheet));
-            $this->numFmtHashTable->addFromSource($this->getWriterPart('Style')->allNumberFormats($this->spreadSheet));
-
-            // Create drawing dictionary
-            $this->drawingHashTable->addFromSource($this->getWriterPart('Drawing')->allDrawings($this->spreadSheet));
-
-            $options = new Archive();
-            $options->setEnableZip64(false);
-            $options->setOutputStream($this->fileHandle);
-
-            $this->zip = new ZipStream(null, $options);
-
-            // Add [Content_Types].xml to ZIP file
-            $this->addZipFile('[Content_Types].xml', $this->getWriterPart('ContentTypes')->writeContentTypes($this->spreadSheet, $this->includeCharts));
-
-            //if hasMacros, add the vbaProject.bin file, Certificate file(if exists)
-            if ($this->spreadSheet->hasMacros()) {
-                $macrosCode = $this->spreadSheet->getMacrosCode();
-                if ($macrosCode !== null) {
-                    // we have the code ?
-                    $this->addZipFile('xl/vbaProject.bin', $macrosCode); //allways in 'xl', allways named vbaProject.bin
-                    if ($this->spreadSheet->hasMacrosCertificate()) {
-                        //signed macros ?
-                        // Yes : add the certificate file and the related rels file
-                        $this->addZipFile('xl/vbaProjectSignature.bin', $this->spreadSheet->getMacrosCertificate());
-                        $this->addZipFile('xl/_rels/vbaProject.bin.rels', $this->getWriterPart('RelsVBA')->writeVBARelationships($this->spreadSheet));
-                    }
-                }
-            }
-            //a custom UI in this workbook ? add it ("base" xml and additional objects (pictures) and rels)
-            if ($this->spreadSheet->hasRibbon()) {
-                $tmpRibbonTarget = $this->spreadSheet->getRibbonXMLData('target');
-                $this->addZipFile($tmpRibbonTarget, $this->spreadSheet->getRibbonXMLData('data'));
-                if ($this->spreadSheet->hasRibbonBinObjects()) {
-                    $tmpRootPath = dirname($tmpRibbonTarget) . '/';
-                    $ribbonBinObjects = $this->spreadSheet->getRibbonBinObjects('data'); //the files to write
-                    foreach ($ribbonBinObjects as $aPath => $aContent) {
-                        $this->addZipFile($tmpRootPath . $aPath, $aContent);
-                    }
-                    //the rels for files
-                    $this->addZipFile($tmpRootPath . '_rels/' . basename($tmpRibbonTarget) . '.rels', $this->getWriterPart('RelsRibbonObjects')->writeRibbonRelationships($this->spreadSheet));
-                }
-            }
-
-            // Add relationships to ZIP file
-            $this->addZipFile('_rels/.rels', $this->getWriterPart('Rels')->writeRelationships($this->spreadSheet));
-            $this->addZipFile('xl/_rels/workbook.xml.rels', $this->getWriterPart('Rels')->writeWorkbookRelationships($this->spreadSheet));
-
-            // Add document properties to ZIP file
-            $this->addZipFile('docProps/app.xml', $this->getWriterPart('DocProps')->writeDocPropsApp($this->spreadSheet));
-            $this->addZipFile('docProps/core.xml', $this->getWriterPart('DocProps')->writeDocPropsCore($this->spreadSheet));
-            $customPropertiesPart = $this->getWriterPart('DocProps')->writeDocPropsCustom($this->spreadSheet);
-            if ($customPropertiesPart !== null) {
-                $this->addZipFile('docProps/custom.xml', $customPropertiesPart);
-            }
-
-            // Add theme to ZIP file
-            $this->addZipFile('xl/theme/theme1.xml', $this->getWriterPart('Theme')->writeTheme($this->spreadSheet));
-
-            // Add string table to ZIP file
-            $this->addZipFile('xl/sharedStrings.xml', $this->getWriterPart('StringTable')->writeStringTable($this->stringTable));
-
-            // Add styles to ZIP file
-            $this->addZipFile('xl/styles.xml', $this->getWriterPart('Style')->writeStyles($this->spreadSheet));
-
-            // Add workbook to ZIP file
-            $this->addZipFile('xl/workbook.xml', $this->getWriterPart('Workbook')->writeWorkbook($this->spreadSheet, $this->preCalculateFormulas));
-
-            $chartCount = 0;
-            // Add worksheets
-            for ($i = 0; $i < $this->spreadSheet->getSheetCount(); ++$i) {
-                $this->addZipFile('xl/worksheets/sheet' . ($i + 1) . '.xml', $this->getWriterPart('Worksheet')->writeWorksheet($this->spreadSheet->getSheet($i), $this->stringTable, $this->includeCharts));
-                if ($this->includeCharts) {
-                    $charts = $this->spreadSheet->getSheet($i)->getChartCollection();
-                    if (count($charts) > 0) {
-                        foreach ($charts as $chart) {
-                            $this->addZipFile('xl/charts/chart' . ($chartCount + 1) . '.xml', $this->getWriterPart('Chart')->writeChart($chart, $this->preCalculateFormulas));
-                            ++$chartCount;
-                        }
-                    }
-                }
-            }
-
-            $chartRef1 = 0;
-            // Add worksheet relationships (drawings, ...)
-            for ($i = 0; $i < $this->spreadSheet->getSheetCount(); ++$i) {
-                // Add relationships
-                $this->addZipFile('xl/worksheets/_rels/sheet' . ($i + 1) . '.xml.rels', $this->getWriterPart('Rels')->writeWorksheetRelationships($this->spreadSheet->getSheet($i), ($i + 1), $this->includeCharts));
-
-                // Add unparsedLoadedData
-                $sheetCodeName = $this->spreadSheet->getSheet($i)->getCodeName();
-                $unparsedLoadedData = $this->spreadSheet->getUnparsedLoadedData();
-                if (isset($unparsedLoadedData['sheets'][$sheetCodeName]['ctrlProps'])) {
-                    foreach ($unparsedLoadedData['sheets'][$sheetCodeName]['ctrlProps'] as $ctrlProp) {
-                        $this->addZipFile($ctrlProp['filePath'], $ctrlProp['content']);
-                    }
-                }
-                if (isset($unparsedLoadedData['sheets'][$sheetCodeName]['printerSettings'])) {
-                    foreach ($unparsedLoadedData['sheets'][$sheetCodeName]['printerSettings'] as $ctrlProp) {
-                        $this->addZipFile($ctrlProp['filePath'], $ctrlProp['content']);
-                    }
-                }
-
-                $drawings = $this->spreadSheet->getSheet($i)->getDrawingCollection();
-                $drawingCount = count($drawings);
-                if ($this->includeCharts) {
-                    $chartCount = $this->spreadSheet->getSheet($i)->getChartCount();
-                }
-
-                // Add drawing and image relationship parts
-                if (($drawingCount > 0) || ($chartCount > 0)) {
-                    // Drawing relationships
-                    $this->addZipFile('xl/drawings/_rels/drawing' . ($i + 1) . '.xml.rels', $this->getWriterPart('Rels')->writeDrawingRelationships($this->spreadSheet->getSheet($i), $chartRef1, $this->includeCharts));
-
-                    // Drawings
-                    $this->addZipFile('xl/drawings/drawing' . ($i + 1) . '.xml', $this->getWriterPart('Drawing')->writeDrawings($this->spreadSheet->getSheet($i), $this->includeCharts));
-                } elseif (isset($unparsedLoadedData['sheets'][$sheetCodeName]['drawingAlternateContents'])) {
-                    // Drawings
-                    $this->addZipFile('xl/drawings/drawing' . ($i + 1) . '.xml', $this->getWriterPart('Drawing')->writeDrawings($this->spreadSheet->getSheet($i), $this->includeCharts));
-                }
-
-                // Add unparsed drawings
-                if (isset($unparsedLoadedData['sheets'][$sheetCodeName]['Drawings'])) {
-                    foreach ($unparsedLoadedData['sheets'][$sheetCodeName]['Drawings'] as $relId => $drawingXml) {
-                        $drawingFile = array_search($relId, $unparsedLoadedData['sheets'][$sheetCodeName]['drawingOriginalIds']);
-                        if ($drawingFile !== false) {
-                            $drawingFile = ltrim($drawingFile, '.');
-                            $this->addZipFile('xl' . $drawingFile, $drawingXml);
-                        }
-                    }
-                }
-
-                // Add comment relationship parts
-                if (count($this->spreadSheet->getSheet($i)->getComments()) > 0) {
-                    // VML Comments
-                    $this->addZipFile('xl/drawings/vmlDrawing' . ($i + 1) . '.vml', $this->getWriterPart('Comments')->writeVMLComments($this->spreadSheet->getSheet($i)));
-
-                    // Comments
-                    $this->addZipFile('xl/comments' . ($i + 1) . '.xml', $this->getWriterPart('Comments')->writeComments($this->spreadSheet->getSheet($i)));
-                }
-
-                // Add unparsed relationship parts
-                if (isset($unparsedLoadedData['sheets'][$sheetCodeName]['vmlDrawings'])) {
-                    foreach ($unparsedLoadedData['sheets'][$sheetCodeName]['vmlDrawings'] as $vmlDrawing) {
-                        $this->addZipFile($vmlDrawing['filePath'], $vmlDrawing['content']);
-                    }
-                }
-
-                // Add header/footer relationship parts
-                if (count($this->spreadSheet->getSheet($i)->getHeaderFooter()->getImages()) > 0) {
-                    // VML Drawings
-                    $this->addZipFile('xl/drawings/vmlDrawingHF' . ($i + 1) . '.vml', $this->getWriterPart('Drawing')->writeVMLHeaderFooterImages($this->spreadSheet->getSheet($i)));
-
-                    // VML Drawing relationships
-                    $this->addZipFile('xl/drawings/_rels/vmlDrawingHF' . ($i + 1) . '.vml.rels', $this->getWriterPart('Rels')->writeHeaderFooterDrawingRelationships($this->spreadSheet->getSheet($i)));
-
-                    // Media
-                    foreach ($this->spreadSheet->getSheet($i)->getHeaderFooter()->getImages() as $image) {
-                        $this->addZipFile('xl/media/' . $image->getIndexedFilename(), file_get_contents($image->getPath()));
-                    }
-                }
-            }
-
-            // Add media
-            for ($i = 0; $i < $this->getDrawingHashTable()->count(); ++$i) {
-                if ($this->getDrawingHashTable()->getByIndex($i) instanceof WorksheetDrawing) {
-                    $imageContents = null;
-                    $imagePath = $this->getDrawingHashTable()->getByIndex($i)->getPath();
-                    if (strpos($imagePath, 'zip://') !== false) {
-                        $imagePath = substr($imagePath, 6);
-                        $imagePathSplitted = explode('#', $imagePath);
-
-                        $imageZip = new ZipArchive();
-                        $imageZip->open($imagePathSplitted[0]);
-                        $imageContents = $imageZip->getFromName($imagePathSplitted[1]);
-                        $imageZip->close();
-                        unset($imageZip);
-                    } else {
-                        $imageContents = file_get_contents($imagePath);
-                    }
-
-                    $this->addZipFile('xl/media/' . str_replace(' ', '_', $this->getDrawingHashTable()->getByIndex($i)->getIndexedFilename()), $imageContents);
-                } elseif ($this->getDrawingHashTable()->getByIndex($i) instanceof MemoryDrawing) {
-                    ob_start();
-                    call_user_func(
-                        $this->getDrawingHashTable()->getByIndex($i)->getRenderingFunction(),
-                        $this->getDrawingHashTable()->getByIndex($i)->getImageResource()
-                    );
-                    $imageContents = ob_get_contents();
-                    ob_end_clean();
-
-                    $this->addZipFile('xl/media/' . str_replace(' ', '_', $this->getDrawingHashTable()->getByIndex($i)->getIndexedFilename()), $imageContents);
-                }
-            }
-
-            Functions::setReturnDateType($saveDateReturnType);
-            Calculation::getInstance($this->spreadSheet)->getDebugLog()->setWriteDebugLog($saveDebugLog);
-
-            // Close file
-            try {
-                $this->zip->finish();
-            } catch (OverflowException $e) {
-                throw new WriterException('Could not close resource.');
-            }
-
-            $this->maybeCloseFileHandle();
-        } else {
-            throw new WriterException('PhpSpreadsheet object unassigned.');
+        // Create string lookup table
+        $this->stringTable = [];
+        for ($i = 0; $i < $this->spreadSheet->getSheetCount(); ++$i) {
+            $this->stringTable = $this->getWriterPart('StringTable')->createStringTable($this->spreadSheet->getSheet($i), $this->stringTable);
         }
+
+        // Create styles dictionaries
+        $this->styleHashTable->addFromSource($this->getWriterPart('Style')->allStyles($this->spreadSheet));
+        $this->stylesConditionalHashTable->addFromSource($this->getWriterPart('Style')->allConditionalStyles($this->spreadSheet));
+        $this->fillHashTable->addFromSource($this->getWriterPart('Style')->allFills($this->spreadSheet));
+        $this->fontHashTable->addFromSource($this->getWriterPart('Style')->allFonts($this->spreadSheet));
+        $this->bordersHashTable->addFromSource($this->getWriterPart('Style')->allBorders($this->spreadSheet));
+        $this->numFmtHashTable->addFromSource($this->getWriterPart('Style')->allNumberFormats($this->spreadSheet));
+
+        // Create drawing dictionary
+        $this->drawingHashTable->addFromSource($this->getWriterPart('Drawing')->allDrawings($this->spreadSheet));
+
+        $options = new Archive();
+        $options->setEnableZip64(false);
+        $options->setOutputStream($this->fileHandle);
+
+        $this->zip = new ZipStream(null, $options);
+
+        // Add [Content_Types].xml to ZIP file
+        $this->addZipFile('[Content_Types].xml', $this->getWriterPart('ContentTypes')->writeContentTypes($this->spreadSheet, $this->includeCharts));
+
+        //if hasMacros, add the vbaProject.bin file, Certificate file(if exists)
+        if ($this->spreadSheet->hasMacros()) {
+            $macrosCode = $this->spreadSheet->getMacrosCode();
+            if ($macrosCode !== null) {
+                // we have the code ?
+                $this->addZipFile('xl/vbaProject.bin', $macrosCode); //allways in 'xl', allways named vbaProject.bin
+                if ($this->spreadSheet->hasMacrosCertificate()) {
+                    //signed macros ?
+                    // Yes : add the certificate file and the related rels file
+                    $this->addZipFile('xl/vbaProjectSignature.bin', $this->spreadSheet->getMacrosCertificate());
+                    $this->addZipFile('xl/_rels/vbaProject.bin.rels', $this->getWriterPart('RelsVBA')->writeVBARelationships($this->spreadSheet));
+                }
+            }
+        }
+        //a custom UI in this workbook ? add it ("base" xml and additional objects (pictures) and rels)
+        if ($this->spreadSheet->hasRibbon()) {
+            $tmpRibbonTarget = $this->spreadSheet->getRibbonXMLData('target');
+            $this->addZipFile($tmpRibbonTarget, $this->spreadSheet->getRibbonXMLData('data'));
+            if ($this->spreadSheet->hasRibbonBinObjects()) {
+                $tmpRootPath = dirname($tmpRibbonTarget) . '/';
+                $ribbonBinObjects = $this->spreadSheet->getRibbonBinObjects('data'); //the files to write
+                foreach ($ribbonBinObjects as $aPath => $aContent) {
+                    $this->addZipFile($tmpRootPath . $aPath, $aContent);
+                }
+                //the rels for files
+                $this->addZipFile($tmpRootPath . '_rels/' . basename($tmpRibbonTarget) . '.rels', $this->getWriterPart('RelsRibbonObjects')->writeRibbonRelationships($this->spreadSheet));
+            }
+        }
+
+        // Add relationships to ZIP file
+        $this->addZipFile('_rels/.rels', $this->getWriterPart('Rels')->writeRelationships($this->spreadSheet));
+        $this->addZipFile('xl/_rels/workbook.xml.rels', $this->getWriterPart('Rels')->writeWorkbookRelationships($this->spreadSheet));
+
+        // Add document properties to ZIP file
+        $this->addZipFile('docProps/app.xml', $this->getWriterPart('DocProps')->writeDocPropsApp($this->spreadSheet));
+        $this->addZipFile('docProps/core.xml', $this->getWriterPart('DocProps')->writeDocPropsCore($this->spreadSheet));
+        $customPropertiesPart = $this->getWriterPart('DocProps')->writeDocPropsCustom($this->spreadSheet);
+        if ($customPropertiesPart !== null) {
+            $this->addZipFile('docProps/custom.xml', $customPropertiesPart);
+        }
+
+        // Add theme to ZIP file
+        $this->addZipFile('xl/theme/theme1.xml', $this->getWriterPart('Theme')->writeTheme($this->spreadSheet));
+
+        // Add string table to ZIP file
+        $this->addZipFile('xl/sharedStrings.xml', $this->getWriterPart('StringTable')->writeStringTable($this->stringTable));
+
+        // Add styles to ZIP file
+        $this->addZipFile('xl/styles.xml', $this->getWriterPart('Style')->writeStyles($this->spreadSheet));
+
+        // Add workbook to ZIP file
+        $this->addZipFile('xl/workbook.xml', $this->getWriterPart('Workbook')->writeWorkbook($this->spreadSheet, $this->preCalculateFormulas));
+
+        $chartCount = 0;
+        // Add worksheets
+        for ($i = 0; $i < $this->spreadSheet->getSheetCount(); ++$i) {
+            $this->addZipFile('xl/worksheets/sheet' . ($i + 1) . '.xml', $this->getWriterPart('Worksheet')->writeWorksheet($this->spreadSheet->getSheet($i), $this->stringTable, $this->includeCharts));
+            if ($this->includeCharts) {
+                $charts = $this->spreadSheet->getSheet($i)->getChartCollection();
+                if (count($charts) > 0) {
+                    foreach ($charts as $chart) {
+                        $this->addZipFile('xl/charts/chart' . ($chartCount + 1) . '.xml', $this->getWriterPart('Chart')->writeChart($chart, $this->preCalculateFormulas));
+                        ++$chartCount;
+                    }
+                }
+            }
+        }
+
+        $chartRef1 = 0;
+        // Add worksheet relationships (drawings, ...)
+        for ($i = 0; $i < $this->spreadSheet->getSheetCount(); ++$i) {
+            // Add relationships
+            $this->addZipFile('xl/worksheets/_rels/sheet' . ($i + 1) . '.xml.rels', $this->getWriterPart('Rels')->writeWorksheetRelationships($this->spreadSheet->getSheet($i), ($i + 1), $this->includeCharts));
+
+            // Add unparsedLoadedData
+            $sheetCodeName = $this->spreadSheet->getSheet($i)->getCodeName();
+            $unparsedLoadedData = $this->spreadSheet->getUnparsedLoadedData();
+            if (isset($unparsedLoadedData['sheets'][$sheetCodeName]['ctrlProps'])) {
+                foreach ($unparsedLoadedData['sheets'][$sheetCodeName]['ctrlProps'] as $ctrlProp) {
+                    $this->addZipFile($ctrlProp['filePath'], $ctrlProp['content']);
+                }
+            }
+            if (isset($unparsedLoadedData['sheets'][$sheetCodeName]['printerSettings'])) {
+                foreach ($unparsedLoadedData['sheets'][$sheetCodeName]['printerSettings'] as $ctrlProp) {
+                    $this->addZipFile($ctrlProp['filePath'], $ctrlProp['content']);
+                }
+            }
+
+            $drawings = $this->spreadSheet->getSheet($i)->getDrawingCollection();
+            $drawingCount = count($drawings);
+            if ($this->includeCharts) {
+                $chartCount = $this->spreadSheet->getSheet($i)->getChartCount();
+            }
+
+            // Add drawing and image relationship parts
+            if (($drawingCount > 0) || ($chartCount > 0)) {
+                // Drawing relationships
+                $this->addZipFile('xl/drawings/_rels/drawing' . ($i + 1) . '.xml.rels', $this->getWriterPart('Rels')->writeDrawingRelationships($this->spreadSheet->getSheet($i), $chartRef1, $this->includeCharts));
+
+                // Drawings
+                $this->addZipFile('xl/drawings/drawing' . ($i + 1) . '.xml', $this->getWriterPart('Drawing')->writeDrawings($this->spreadSheet->getSheet($i), $this->includeCharts));
+            } elseif (isset($unparsedLoadedData['sheets'][$sheetCodeName]['drawingAlternateContents'])) {
+                // Drawings
+                $this->addZipFile('xl/drawings/drawing' . ($i + 1) . '.xml', $this->getWriterPart('Drawing')->writeDrawings($this->spreadSheet->getSheet($i), $this->includeCharts));
+            }
+
+            // Add unparsed drawings
+            if (isset($unparsedLoadedData['sheets'][$sheetCodeName]['Drawings'])) {
+                foreach ($unparsedLoadedData['sheets'][$sheetCodeName]['Drawings'] as $relId => $drawingXml) {
+                    $drawingFile = array_search($relId, $unparsedLoadedData['sheets'][$sheetCodeName]['drawingOriginalIds']);
+                    if ($drawingFile !== false) {
+                        $drawingFile = ltrim($drawingFile, '.');
+                        $this->addZipFile('xl' . $drawingFile, $drawingXml);
+                    }
+                }
+            }
+
+            // Add comment relationship parts
+            if (count($this->spreadSheet->getSheet($i)->getComments()) > 0) {
+                // VML Comments
+                $this->addZipFile('xl/drawings/vmlDrawing' . ($i + 1) . '.vml', $this->getWriterPart('Comments')->writeVMLComments($this->spreadSheet->getSheet($i)));
+
+                // Comments
+                $this->addZipFile('xl/comments' . ($i + 1) . '.xml', $this->getWriterPart('Comments')->writeComments($this->spreadSheet->getSheet($i)));
+            }
+
+            // Add unparsed relationship parts
+            if (isset($unparsedLoadedData['sheets'][$sheetCodeName]['vmlDrawings'])) {
+                foreach ($unparsedLoadedData['sheets'][$sheetCodeName]['vmlDrawings'] as $vmlDrawing) {
+                    $this->addZipFile($vmlDrawing['filePath'], $vmlDrawing['content']);
+                }
+            }
+
+            // Add header/footer relationship parts
+            if (count($this->spreadSheet->getSheet($i)->getHeaderFooter()->getImages()) > 0) {
+                // VML Drawings
+                $this->addZipFile('xl/drawings/vmlDrawingHF' . ($i + 1) . '.vml', $this->getWriterPart('Drawing')->writeVMLHeaderFooterImages($this->spreadSheet->getSheet($i)));
+
+                // VML Drawing relationships
+                $this->addZipFile('xl/drawings/_rels/vmlDrawingHF' . ($i + 1) . '.vml.rels', $this->getWriterPart('Rels')->writeHeaderFooterDrawingRelationships($this->spreadSheet->getSheet($i)));
+
+                // Media
+                foreach ($this->spreadSheet->getSheet($i)->getHeaderFooter()->getImages() as $image) {
+                    $this->addZipFile('xl/media/' . $image->getIndexedFilename(), file_get_contents($image->getPath()));
+                }
+            }
+        }
+
+        // Add media
+        for ($i = 0; $i < $this->getDrawingHashTable()->count(); ++$i) {
+            if ($this->getDrawingHashTable()->getByIndex($i) instanceof WorksheetDrawing) {
+                $imageContents = null;
+                $imagePath = $this->getDrawingHashTable()->getByIndex($i)->getPath();
+                if (strpos($imagePath, 'zip://') !== false) {
+                    $imagePath = substr($imagePath, 6);
+                    $imagePathSplitted = explode('#', $imagePath);
+
+                    $imageZip = new ZipArchive();
+                    $imageZip->open($imagePathSplitted[0]);
+                    $imageContents = $imageZip->getFromName($imagePathSplitted[1]);
+                    $imageZip->close();
+                    unset($imageZip);
+                } else {
+                    $imageContents = file_get_contents($imagePath);
+                }
+
+                $this->addZipFile('xl/media/' . str_replace(' ', '_', $this->getDrawingHashTable()->getByIndex($i)->getIndexedFilename()), $imageContents);
+            } elseif ($this->getDrawingHashTable()->getByIndex($i) instanceof MemoryDrawing) {
+                ob_start();
+                call_user_func(
+                    $this->getDrawingHashTable()->getByIndex($i)->getRenderingFunction(),
+                    $this->getDrawingHashTable()->getByIndex($i)->getImageResource()
+                );
+                $imageContents = ob_get_contents();
+                ob_end_clean();
+
+                $this->addZipFile('xl/media/' . str_replace(' ', '_', $this->getDrawingHashTable()->getByIndex($i)->getIndexedFilename()), $imageContents);
+            }
+        }
+
+        Functions::setReturnDateType($saveDateReturnType);
+        Calculation::getInstance($this->spreadSheet)->getDebugLog()->setWriteDebugLog($saveDebugLog);
+
+        // Close file
+        try {
+            $this->zip->finish();
+        } catch (OverflowException $e) {
+            throw new WriterException('Could not close resource.');
+        }
+
+        $this->maybeCloseFileHandle();
     }
 
     /**
@@ -419,11 +415,7 @@ class Xlsx extends BaseWriter
      */
     public function getSpreadsheet()
     {
-        if ($this->spreadSheet !== null) {
-            return $this->spreadSheet;
-        }
-
-        throw new WriterException('No Spreadsheet object assigned.');
+        return $this->spreadSheet;
     }
 
     /**
diff --git a/tests/PhpSpreadsheetTests/Style/FontTest.php b/tests/PhpSpreadsheetTests/Style/FontTest.php
new file mode 100644
index 00000000..c014a4b6
--- /dev/null
+++ b/tests/PhpSpreadsheetTests/Style/FontTest.php
@@ -0,0 +1,42 @@
+<?php
+
+namespace PhpOffice\PhpSpreadsheetTests\Style;
+
+use PhpOffice\PhpSpreadsheet\Spreadsheet;
+use PHPUnit\Framework\TestCase;
+
+class FontTest extends TestCase
+{
+    public function testSuperSubScript(): void
+    {
+        $spreadsheet = new Spreadsheet();
+        $sheet = $spreadsheet->getActiveSheet();
+        $cell = $sheet->getCell('A1');
+        $cell->setValue('Cell A1');
+        $font = $cell->getStyle()->getFont();
+        $font->setSuperscript(true);
+        $font->setSubscript(true);
+        self::assertFalse($font->getSuperscript(), 'Earlier set true loses');
+        self::assertTrue($font->getSubscript(), 'Last set true wins');
+        $font->setSubscript(true);
+        $font->setSuperscript(true);
+        self::assertTrue($font->getSuperscript(), 'Last set true wins');
+        self::assertFalse($font->getSubscript(), 'Earlier set true loses');
+        $font->setSuperscript(false);
+        $font->setSubscript(false);
+        self::assertFalse($font->getSuperscript(), 'False remains unchanged');
+        self::assertFalse($font->getSubscript(), 'False remains unchanged');
+        $font->setSubscript(false);
+        $font->setSuperscript(false);
+        self::assertFalse($font->getSuperscript(), 'False remains unchanged');
+        self::assertFalse($font->getSubscript(), 'False remains unchanged');
+        $font->setSubscript(true);
+        $font->setSuperscript(false);
+        self::assertFalse($font->getSuperscript(), 'False remains unchanged');
+        self::assertTrue($font->getSubscript(), 'True remains unchanged');
+        $font->setSubscript(false);
+        $font->setSuperscript(true);
+        self::assertTrue($font->getSuperscript());
+        self::assertFalse($font->getSubscript(), 'False remains unchanged');
+    }
+}