Tests run successfully as if there is a headful environment but all the captured screenshots are black.

java.awt.Robot.createScreenCapture(rectangle) method is used.

Here is the scenario to reproduce:

Use Remote Desktop connection to run the app that is taking the screenshot.
Leave it running and disconnect the session.
Screenshots obtained after the disconnection will be black.

Similar scenario is jenkins build running on the Windows Server 2012. It won't fail with headless exception but all the screenshots will be black.

I believe Robot should throw an exception rather than returning all black screenshots.