fixed issue with empty slug

README.md

@@ -15,3 +15,5 @@ Contributions and Bugs
 ----------------------
 
 If you have ideas on how to improve the library or if you discover a bug, I would appreciate if you shared them with me, right here on Github. In either case, please open a new issue [here](https://github.com/felixarntz/wpdlib/issues/new)!
+
+You can also contribute to the library by translating it. Among the library files, there is a `.pot` file which you can use as a starting point. When you're done with a translation, you can either create a pull request with the new translation files or you can send them to me manually.

inc/WPDLib/Components/Base.php

@@ -266,13 +266,16 @@ public function get_parent( $index = 0, $depth = 1 ) {
 		 * @return bool|WPDLib\Util\Error an error object if an error occurred during validation, true if it was validated, false if it did not need to be validated
 		 */
 		public function validate( $parent = null ) {
-			if ( $parent !== null ) {
+			if ( null !== $parent ) {
 				if ( count( $this->parents ) > 0 && ! $this->supports_multiparents() ) {
 					return new UtilError( 'no_multiparent_component', sprintf( __( 'The component %1$s of class %2$s already has a parent assigned and is not a multiparent component.', 'wpdlib' ), $this->slug, get_class( $this ) ), '', ComponentManager::get_scope() );
 				}
 				$this->parents[ $parent->slug ] = $parent;
 			}
 			if ( ! $this->validated ) {
+				if ( empty( $this->slug ) ) {
+					return new UtilError( 'empty_slug_component', __( 'A component with an empty slug is not allowed.', 'wpdlib' ), '', ComponentManager::get_scope() );
+				}
 				$defaults = $this->get_defaults();
 				foreach ( $defaults as $key => $default ) {
 					if ( ! isset( $this->args[ $key ] ) ) {
@@ -295,9 +298,10 @@ public function validate( $parent = null ) {
 		 * Checks if the slug of the component is valid.
 		 *
 		 * @since 0.5.0
+		 * @param WPDLib\Components\Base $parent the parent component of the component
 		 * @return bool whether the component slug is valid
 		 */
-		public function is_valid_slug() {
+		public function is_valid_slug( $parent = null ) {
 			if ( $this->valid_slug === null ) {
 				$globalnames = $this->supports_globalslug();
 				if ( $globalnames !== true ) {

inc/WPDLib/Components/Menu.php

@@ -90,7 +90,7 @@ public function is_already_added( $screen_slug ) {
 		/**
 		 * Creates the admin menu.
 		 *
-		 * If the menu has an empty slug, the children are added as a page, but not added into any menu.
+		 * If the menu has the slug 'none', the children are added as a page, but not added into any menu.
 		 * Otherwise the children will simply be added to the menu. The first child will be added using `add_menu_page()`.
 		 *
 		 * @since 0.5.0
@@ -101,7 +101,7 @@ public function is_already_added( $screen_slug ) {
 		public function create() {
 			foreach ( $this->get_children() as $menu_item ) {
 				if ( is_callable( array( $menu_item, 'add_to_menu' ) ) ) {
-					if ( empty( $this->slug ) ) {
+					if ( 'none' == $this->slug ) {
 						$this->add_non_menu_page( $menu_item );
 					} elseif ( ! $this->is_already_added( $menu_item->slug ) ) {
 						$this->add_menu_page( $menu_item );
@@ -346,7 +346,7 @@ protected function add_submenu_page( $menu_item ) {
 		/**
 		 * Adds a new page to the WordPress admin which should not be part of any menu.
 		 *
-		 * This function is only used for the special case when a menu component's slug is empty.
+		 * This function is only used for the special case when a menu component's slug is set to 'none'.
 		 * This allows you to add pages that are not visible in any menu.
 		 *
 		 * @since 0.5.0