I don't have a clue why anyone would ask about desiccant when the question was about an empty connector. Here's my best guess in answer to the original question...
My HF ham radios often come with empty connectors such as this on the circuit boards for optional accessories that can be purchased and added later, not that anyone will open up a drone controller to do this kind of thing. The only other thing I can think of is that is many purchase a non-+ version to be used with tablet or smart phone external display. This may be the connection to connect through the case to the external display. If anyone reading this has the external display controller, does the location of the plug match where the display cable plugs in?