public function selectHeaderContentType($contentType) {
		if (count($contentType) === 0 or (count($contentType) === 1 and $contentType[0] === '')) {
			return 'application/json';
		} elseif (preg_grep("/application\/json/i", $contentType)) {
			return 'application/json';
		} else {
			return implode(',', $contentType);
		}
	}