Ensure that `role` is not empty before adding it in `add_role()` function and methods.

Props MikeHansenMe, dannydehaan, michielhab.
Fixes #23746.

Built from https://develop.svn.wordpress.org/trunk@33967


git-svn-id: http://core.svn.wordpress.org/trunk@33936 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/capabilities-functions.php

@@ -471,6 +471,9 @@ function get_role( $role ) {
  * @return WP_Role|null WP_Role object if role is added, null if already exists.
  */
 function add_role( $role, $display_name, $capabilities = array() ) {
+	if ( empty( $role ) ) {
+		return;
+	}
 	return wp_roles()->add_role( $role, $display_name, $capabilities );
 }
 

wp-includes/class-wp-roles.php

@@ -172,8 +172,9 @@ class WP_Roles {
 	 * @return WP_Role|void WP_Role object, if role is added.
 	 */
 	public function add_role( $role, $display_name, $capabilities = array() ) {
-		if ( isset( $this->roles[$role] ) )
+		if ( empty( $role ) || isset( $this->roles[ $role ] ) ) {
 			return;
+		}
 
 		$this->roles[$role] = array(
 			'name' => $display_name,

wp-includes/class-wp-user.php

@@ -439,6 +439,10 @@ class WP_User {
 	 * @param string $role Role name.
 	 */
 	public function add_role( $role ) {
+		if ( empty( $role ) ) {
+			return;
+		}
+
 		$this->caps[$role] = true;
 		update_user_meta( $this->ID, $this->cap_key, $this->caps );
 		$this->get_role_caps();

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.4-alpha-33966';
+$wp_version = '4.4-alpha-33967';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.