Apply custom style to empty cells if needed (#307)

Fixes #295

If a row should be written with a custom style, the handling of empty cells should change.
Instead of being skipped entirely, empty cells will be applied the custom style, if this style has custom background color or borders.
If not, then the cell definition can still be skipped.

src/Spout/Writer/XLSX/Internal/Workbook.php

@@ -86,7 +86,7 @@ class Workbook extends AbstractWorkbook
         $sheet = new Sheet($newSheetIndex);
 
         $worksheetFilesFolder = $this->fileSystemHelper->getXlWorksheetsFolder();
-        $worksheet = new Worksheet($sheet, $worksheetFilesFolder, $this->sharedStringsHelper, $this->shouldUseInlineStrings);
+        $worksheet = new Worksheet($sheet, $worksheetFilesFolder, $this->sharedStringsHelper, $this->styleHelper, $this->shouldUseInlineStrings);
         $this->worksheets[] = $worksheet;
 
         return $worksheet;

src/Spout/Writer/XLSX/Internal/Worksheet.php

@@ -30,6 +30,9 @@ EOD;
     /** @var \Box\Spout\Writer\XLSX\Helper\SharedStringsHelper Helper to write shared strings */
     protected $sharedStringsHelper;
 
+    /** @var \Box\Spout\Writer\XLSX\Helper\StyleHelper Helper to work with styles */
+    protected $styleHelper;
+
     /** @var bool Whether inline or shared strings should be used */
     protected $shouldUseInlineStrings;
 
@@ -46,13 +49,15 @@ EOD;
      * @param \Box\Spout\Writer\Common\Sheet $externalSheet The associated "external" sheet
      * @param string $worksheetFilesFolder Temporary folder where the files to create the XLSX will be stored
      * @param \Box\Spout\Writer\XLSX\Helper\SharedStringsHelper $sharedStringsHelper Helper for shared strings
+     * @param \Box\Spout\Writer\XLSX\Helper\StyleHelper Helper to work with styles
      * @param bool $shouldUseInlineStrings Whether inline or shared strings should be used
      * @throws \Box\Spout\Common\Exception\IOException If the sheet data file cannot be opened for writing
      */
-    public function __construct($externalSheet, $worksheetFilesFolder, $sharedStringsHelper, $shouldUseInlineStrings)
+    public function __construct($externalSheet, $worksheetFilesFolder, $sharedStringsHelper, $styleHelper, $shouldUseInlineStrings)
     {
         $this->externalSheet = $externalSheet;
         $this->sharedStringsHelper = $sharedStringsHelper;
+        $this->styleHelper = $styleHelper;
         $this->shouldUseInlineStrings = $shouldUseInlineStrings;
 
         /** @noinspection PhpUnnecessaryFullyQualifiedNameInspection */
@@ -177,8 +182,13 @@ EOD;
         } else if (CellHelper::isNumeric($cellValue)) {
             $cellXML .= '><v>' . $cellValue . '</v></c>';
         } else if (empty($cellValue)) {
-            // don't write empty cells (not appending to $cellXML is the right behavior!)
-            $cellXML = '';
+            if ($this->styleHelper->shouldApplyStyleOnEmptyCell($styleId)) {
+                $cellXML .= '/>';
+            } else {
+                // don't write empty cells that do no need styling
+                // NOTE: not appending to $cellXML is the right behavior!!
+                $cellXML = '';
+            }
         } else {
             throw new InvalidArgumentException('Trying to add a value with an unsupported type: ' . gettype($cellValue));
         }