Cara Memperbaiki WordPress Call to undefined method WP_Error

<?php

class WP_Error {
	
	public $errors = array();

	public $error_data = array();

	protected $additional_data = array();

	public function __construct( $code = '', $message = '', $data = '' ) {
		if ( empty( $code ) ) {
			return;
		}

		$this->add( $code, $message, $data );
	}

	public function get_error_codes() {
		if ( ! $this->has_errors() ) {
			return array();
		}

		return array_keys( $this->errors );
	}

	public function get_error_code() {
		$codes = $this->get_error_codes();

		if ( empty( $codes ) ) {
			return '';
		}

		return $codes[0];
	}

	public function get_error_messages( $code = '' ) {
		// Return all messages if no code specified.
		if ( empty( $code ) ) {
			$all_messages = array();
			foreach ( (array) $this->errors as $code => $messages ) {
				$all_messages = array_merge( $all_messages, $messages );
			}

			return $all_messages;
		}

		if ( isset( $this->errors[ $code ] ) ) {
			return $this->errors[ $code ];
		} else {
			return array();
		}
	}

	public function get_error_message( $code = '' ) {
		if ( empty( $code ) ) {
			$code = $this->get_error_code();
		}
		$messages = $this->get_error_messages( $code );
		if ( empty( $messages ) ) {
			return '';
		}
		return $messages[0];
	}

	public function get_error_data( $code = '' ) {
		if ( empty( $code ) ) {
			$code = $this->get_error_code();
		}

		if ( isset( $this->error_data[ $code ] ) ) {
			return $this->error_data[ $code ];
		}
	}

	public function has_errors() {
		if ( ! empty( $this->errors ) ) {
			return true;
		}
		return false;
	}

	public function add( $code, $message, $data = '' ) {
		$this->errors[ $code ][] = $message;

		if ( ! empty( $data ) ) {
			$this->add_data( $data, $code );
		}

		do_action( 'wp_error_added', $code, $message, $data, $this );
	}

	public function add_data( $data, $code = '' ) {
		if ( empty( $code ) ) {
			$code = $this->get_error_code();
		}

		if ( isset( $this->error_data[ $code ] ) ) {
			$this->additional_data[ $code ][] = $this->error_data[ $code ];
		}

		$this->error_data[ $code ] = $data;
	}

	public function get_all_error_data( $code = '' ) {
		if ( empty( $code ) ) {
			$code = $this->get_error_code();
		}

		$data = array();

		if ( isset( $this->additional_data[ $code ] ) ) {
			$data = $this->additional_data[ $code ];
		}

		if ( isset( $this->error_data[ $code ] ) ) {
			$data[] = $this->error_data[ $code ];
		}

		return $data;
	}

	public function remove( $code ) {
		unset( $this->errors[ $code ] );
		unset( $this->error_data[ $code ] );
		unset( $this->additional_data[ $code ] );
	}

	public function merge_from( WP_Error $error ) {
		static::copy_errors( $error, $this );
	}

	public function export_to( WP_Error $error ) {
		static::copy_errors( $this, $error );
	}

	protected static function copy_errors( WP_Error $from, WP_Error $to ) {
		foreach ( $from->get_error_codes() as $code ) {
			foreach ( $from->get_error_messages( $code ) as $error_message ) {
				$to->add( $code, $error_message );
			}

			foreach ( $from->get_all_error_data( $code ) as $data ) {
				$to->add_data( $data, $code );
			}
		}
	}
}