Docx::getMimeType

protected function getMimeType(File $file): ?string
{
	$types = $this->getPrintableMimeTypes();

	$mimeType = $file->getContentType();
	if(isset($types[$mimeType]))
	{
		return $mimeType;
	}

	$extension = $file->getExtension();
	if(!empty($extension))
	{
		$types = array_flip($types);
		if(isset($types[$extension]))
		{
			return $types[$extension];
		}
	}

	return null;
}