public function mergeCells($pRange)
    {
        // Uppercase coordinate
        $pRange = strtoupper($pRange);

        if (strpos($pRange, ':') !== false) {
            $this->mergeCells[$pRange] = $pRange;

            // make sure cells are created

            // get the cells in the range
            $aReferences = Coordinate::extractAllCellReferencesInRange($pRange);

            // create upper left cell if it does not already exist
            $upperLeft = $aReferences[0];
            if (!$this->cellExists($upperLeft)) {
                $this->getCell($upperLeft)->setValueExplicit(null, DataType::TYPE_NULL);
            }

            // Blank out the rest of the cells in the range (if they exist)
            $count = count($aReferences);
            for ($i = 1; $i < $count; ++$i) {
                if ($this->cellExists($aReferences[$i])) {
                    $this->getCell($aReferences[$i])->setValueExplicit(null, DataType::TYPE_NULL);
                }
            }
        } else {
            throw new Exception('Merge must be set on a range of cells.');
        }

        return $this;
    }