public static function merge_custom_array( $custom, $base = array(), $flip = true ) {
		if ( true === $flip ) {
			$base = array_filter( $base );
		}

		if ( empty( $custom ) || ! \is_array( $custom ) ) {
			return $base;
		}

		if ( true === $flip ) {
			$custom = array_fill_keys( $custom, false );
		}

		if ( empty( $base ) ) {
			return $custom;
		}

		return array_merge( $base, $custom );
	}