command <TAB> ==> options should be listed, argument completer returns no value.
I remember that it used to work, but recently it doesn't anymore.
When the following check occurs AeshCommandLineCompletionParser line 220
if(!haveCompletion && !arg.isRequired() && arg.getValue() != null &&
parser.getProcessedCommand().completeStatus().value() == null)

{ doListOptions(completeOperation, ""); }

parser.getProcessedCommand().completeStatus().value() returns the empty string.

So the test is false and options are not completed.