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

Props MikeHansenMe, dannydehaan, michielhab.
Fixes #23746.


git-svn-id: https://develop.svn.wordpress.org/trunk@33967 602fd350-edb4-49c9-b593-d223f7449a82

src/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 );
 }