public function mergeQueryAttribute( $old, $new ) {
		if ( $new === null ) {
			return $old;
		}

		if ( $old === null ) {
			return $new;
		}

		return function ( $query_vars ) use ( $old, $new ) {
			return call_user_func( $new, call_user_func( $old, $query_vars ) );
		};
	}
public function mergeQueryAttribute( $old, $new ) {
		if ( $new === null ) {
			return $old;
		}

		if ( $old === null ) {
			return $new;
		}

		return function ( $query_vars ) use ( $old, $new ) {
			return call_user_func( $new, call_user_func( $old, $query_vars ) );
		};
	}
public function mergeQueryAttribute ( $ old , $ new ) { if ( $ new === null ) { return $ old ; } if ( $ old === null ) { return $ new ; } return function ( $ query_vars ) use ( $ old , $ new ) { return call_user_func ( $ new , call_user_func ( $ old , $ query_vars ) ) ; } ; }
Merge the handler attribute taking the latest value.

@param  callable|null $old
@param  callable|null $new
@return string|\Closure
Merge the handler attribute taking the latest value .