public function getPriorities()
	{
		// Fetch priorities when the method is called for the first time.
		if ( $this->priorities === null ) {
			$priorities = array();
			$result = $this->api(self::REQUEST_GET, '/rest/api/2/priority', array(), true);

			/* set hash key as custom field id */
			foreach ( $result as $priority ) {
				$priorities[$priority['id']] = $priority;
			}

			$this->priorities = $priorities;
		}

		return $this->priorities;
	}