Create Article menu item: displays error if Category is not selected when Default Category is set

administrator/language/en-GB/en-GB.com_content.ini

@@ -34,6 +34,7 @@ COM_CONTENT_CREATE_ARTICLE_CATEGORY_LABEL="Default Category"
 COM_CONTENT_CREATE_ARTICLE_CATEGORY_DESC="If set to 'Yes', this page will only let you create articles in the category selected below."
 COM_CONTENT_CREATE_ARTICLE_CUSTOM_CANCEL_REDIRECT_DESC="If set to 'Yes', you can set a redirection page, distinct from above 'Submission/Cancel Redirect', to redirect to when user Cancels article submission.<br />If set to 'No', when user Cancels article submission, the user is redirected to the above 'Submission/Cancel Redirect' page."
 COM_CONTENT_CREATE_ARTICLE_CUSTOM_CANCEL_REDIRECT_LABEL="Custom Redirect on Cancel"
+COM_CONTENT_CREATE_ARTICLE_ERROR="When default category is enabled, a category should be selected."
 COM_CONTENT_CREATE_ARTICLE_REDIRECTMENU_DESC="Select the page the user will be redirected to after a successful article submission and after cancel (if not set differently below). The default is to redirect to the home page."
 COM_CONTENT_CREATE_ARTICLE_REDIRECTMENU_LABEL="Submission/Cancel Redirect"
 COM_CONTENT_DRILL_CATEGORIES_LABEL="List or Blog: after choosing the display,<br />make sure you define the Options in the desired layout."

plugins/content/joomla/joomla.php

@@ -299,4 +299,40 @@ public function onContentChangeState($context, $pks, $value)
 
 		return true;
 	}
+
+	/**
+	* The save event.
+	*
+	* @param   string   $context  The context
+	* @param   object   $table    The item
+	* @param   boolean  $isNew    Is new item
+	*
+	* @return  void
+	*
+	* @since   __DEPLOY_VERSION__
+	*/
+	public function onContentBeforeSave($context, $table, $isNew)
+	{
+		// Check we are handling the frontend edit form.
+		if ($context !== 'com_menus.item')
+		{
+			return true;
+		}
+
+		// Special case for Create article menu item
+		if ($table->link !== 'index.php?option=com_content&view=form&layout=edit')
+		{
+			return true;
+		}
+
+		// Display error if catid is not set when enable_category is enabled
+		$params = json_decode($table->params, true);
+
+		if ($params['enable_category'] == 1 && empty($params['catid']))
+		{
+			$table->setError(JText::_('COM_CONTENT_CREATE_ARTICLE_ERROR'));
+
+			return false;
+		}
+	}
 }