code: public function fromArray(array $source, $nullValue = null, $startCell = 'A1', $strictNullComparison = false)
      {
          //    Convert a 1-D array to 2-D (for ease of looping)
          if (!is_array(end($source))) {
              $source = [$source];
          }
  
          // start coordinate
          list($startColumn, $startRow) = Coordinate::coordinateFromString($startCell);
  
          // Loop through $source
          foreach ($source as $rowData) {
              $currentColumn = $startColumn;
              foreach ($rowData as $cellValue) {
                  if ($strictNullComparison) {
                      if ($cellValue !== $nullValue) {
                          // Set cell value
                          $this->getCell($currentColumn . $startRow)->setValue($cellValue);
                      }
                  } else {
                      if ($cellValue != $nullValue) {
                          // Set cell value
                          $this->getCell($currentColumn . $startRow)->setValue($cellValue);
                      }
                  }
                  ++$currentColumn;
              }
              ++$startRow;
          }
  
          return $this;
      }
docs: Fill worksheet from values in array.
  
  @param array $source Source array
  @param mixed $nullValue Value in source array that stands for blank cell
  @param string $startCell Insert array starting from this cell address as the top left coordinate
  @param bool $strictNullComparison Apply strict comparison when testing for null values in the array
  
  @throws Exception
  
  @return Worksheet