Empty Widget error is issued in the following situations:
<Dropdown> has no content. Please add some content.
You have a Dropdown widget that does not include any widget to display the values.
Place a widget inside the Dropdown to display the values to the end-user, such as an Expression. If the properties Variable, List and Values of the Dropdown are blank, you can also drag and drop a variable of type Entity or Static Entity Identifier into the Dropdown to automatically configure the Dropdown to present the records of the Entity or Static Entity.
Double-click on the error line to take you directly to the source of the error.