Hover over undefined variable shows empty box

[hoehrmann]

When you hover over a variable that is undefined, you get a tiny empty box. It should probably show undef (and when the value is a string, put quote marks around it, so users can tell the string "undef" apart from the value undef).

[hoehrmann]

This turned out (the hard way) to be a symptom of a more general problem. Apparently there is an unwritten assumption that debug adapters generate eval-able strings in various places, https://github.com/Microsoft/debug-adapter-protocol/issues/36 including the data for hover.