protected function checkMultipartParams( $params ) {
		foreach ( $params as $key => $val ) {
			if ( !is_array( $val ) ) {
				throw new Exception( "Parameter '$key' must be an array." );
			}
			if ( !in_array( $key, array_keys( $this->getParams() ) ) ) {
				throw new Exception( "Parameter '$key' is not already set on this request." );
			}
		}
	}