From dfbe885115b8c1f6dbbbf3e0bd19f9ddc7321895 Mon Sep 17 00:00:00 2001
From: Daniel Bachhuber <danielbachhuber@git.wordpress.org>
Date: Tue, 23 Oct 2018 18:55:45 +0000
Subject: [PATCH] Meta: Allow empty strings to be set by Custom Fields meta
 box.

Because the REST API allows meta keys to have empty values, the Custom Fields meta box should permit the same behavior.

Props charlestonsw, soulseekah.
Fixes #43559.


git-svn-id: https://develop.svn.wordpress.org/branches/5.0@43811 602fd350-edb4-49c9-b593-d223f7449a82
---
 src/wp-admin/includes/ajax-actions.php     |  2 -
 src/wp-admin/includes/post.php             |  2 +-
 tests/phpunit/tests/admin/includesPost.php | 17 ++++++
 tests/phpunit/tests/ajax/AddMeta.php       | 71 ++++++++++++++++++++++
 4 files changed, 89 insertions(+), 3 deletions(-)
 create mode 100644 tests/phpunit/tests/ajax/AddMeta.php

diff --git a/src/wp-admin/includes/ajax-actions.php b/src/wp-admin/includes/ajax-actions.php
index 8fb348c6d387..fcc67eba1944 100644
--- a/src/wp-admin/includes/ajax-actions.php
+++ b/src/wp-admin/includes/ajax-actions.php
@@ -1341,8 +1341,6 @@ function wp_ajax_add_meta() {
 		$value = wp_unslash( $_POST['meta'][$mid]['value'] );
 		if ( '' == trim($key) )
 			wp_die( __( 'Please provide a custom field name.' ) );
-		if ( '' == trim($value) )
-			wp_die( __( 'Please provide a custom field value.' ) );
 		if ( ! $meta = get_metadata_by_mid( 'post', $mid ) )
 			wp_die( 0 ); // if meta doesn't exist
 		if ( is_protected_meta( $meta->meta_key, 'post' ) || is_protected_meta( $key, 'post' ) ||
diff --git a/src/wp-admin/includes/post.php b/src/wp-admin/includes/post.php
index 015c7d32ec9f..a95ff78bc696 100644
--- a/src/wp-admin/includes/post.php
+++ b/src/wp-admin/includes/post.php
@@ -814,7 +814,7 @@ function add_meta( $post_ID ) {
 	if ( is_string( $metavalue ) )
 		$metavalue = trim( $metavalue );
 
-	if ( ('0' === $metavalue || ! empty ( $metavalue ) ) && ( ( ( '#NONE#' != $metakeyselect ) && !empty ( $metakeyselect) ) || !empty ( $metakeyinput ) ) ) {
+	if ( ( ( '#NONE#' != $metakeyselect ) && ! empty( $metakeyselect ) ) || ! empty( $metakeyinput ) ) {
 		/*
 		 * We have a key/value pair. If both the select and the input
 		 * for the key have data, the input takes precedence.
diff --git a/tests/phpunit/tests/admin/includesPost.php b/tests/phpunit/tests/admin/includesPost.php
index f57b27f203e0..3d782e2dba69 100644
--- a/tests/phpunit/tests/admin/includesPost.php
+++ b/tests/phpunit/tests/admin/includesPost.php
@@ -707,4 +707,21 @@ function test_get_block_editor_server_block_settings() {
 		$this->assertArrayHasKey( $name, $blocks );
 		$this->assertSame( array( 'icon' => 'text' ), $blocks[ $name ] );
 	}
+
+	/**
+	 * @ticket 43559
+	 */
+	public function test_post_add_meta_empty_is_allowed() {
+		$p     = self::factory()->post->create();
+
+		$_POST = array(
+			'metakeyinput' => 'testkey',
+			'metavalue'    => '',
+		);
+
+		wp_set_current_user( self::$admin_id );
+
+		$this->assertNotFalse( add_meta( $p ) );
+		$this->assertEquals( '', get_post_meta( $p, 'testkey', true ) );
+	}
 }
diff --git a/tests/phpunit/tests/ajax/AddMeta.php b/tests/phpunit/tests/ajax/AddMeta.php
new file mode 100644
index 000000000000..a20deede629c
--- /dev/null
+++ b/tests/phpunit/tests/ajax/AddMeta.php
@@ -0,0 +1,71 @@
+<?php
+
+/**
+ * Admin ajax functions to be tested
+ */
+require_once( ABSPATH . 'wp-admin/includes/ajax-actions.php' );
+
+/**
+ * Testing Add Meta AJAX functionality.
+ *
+ * @group ajax
+ */
+class Tests_Ajax_AddMeta extends WP_Ajax_UnitTestCase {
+	/**
+	 * @ticket 43559
+	 */
+	public function test_post_add_meta_empty_is_allowed_ajax() {
+		$p = self::factory()->post->create();
+
+		// Become an administrator.
+		$this->_setRole( 'administrator' );
+
+		$_POST = array(
+			'post_id'      => $p,
+			'metakeyinput' => 'testkey',
+			'metavalue'    => '',
+			'_ajax_nonce-add-meta' => wp_create_nonce( 'add-meta' ),
+		);
+
+		// Make the request.
+		try {
+			$this->_handleAjax( 'add-meta' );
+		} catch ( WPAjaxDieContinueException $e ) {
+			unset( $e );
+		}
+
+		$this->assertEquals( '', get_post_meta( $p, 'testkey', true ) );
+	}
+
+	/**
+	 * @ticket 43559
+	 */
+	public function test_post_update_meta_empty_is_allowed_ajax() {
+		$p = self::factory()->post->create();
+
+		$m = add_post_meta( $p, 'testkey', 'hello' );
+
+		// Become an administrator.
+		$this->_setRole( 'administrator' );
+
+		$_POST = array(
+			'_ajax_nonce-add-meta' => wp_create_nonce( 'add-meta' ),
+			'post_id' => $p,
+			'meta' => array(
+				$m => array(
+					'key'   => 'testkey',
+					'value' => '',
+				),
+			),
+		);
+
+		// Make the request.
+		try {
+			$this->_handleAjax( 'add-meta' );
+		} catch ( WPAjaxDieContinueException $e ) {
+			unset( $e );
+		}
+
+		$this->assertEquals( '', get_post_meta( $p, 'testkey', true ) );
+	}
+}