No visual indicator when dragging on an empty FB interface
Issue
When dragging events or in/output onto a FB interface, a line is shown to indicate its position relative to other existing elements. When the FB does not yet have events or data, no such line is shown though. To identify whether for example the data is input or output, and to show that the new element is dragged close enough to the interface, a line would be helpful even when there are no other elements present.
Solution
Add a line when dragging an element onto a FB interface.