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.