Negative numbers mistaken for options

If an option has a negative numerical argument, the parser mistakes it for another option and throws an error. For example, consider:

Argument numArg = aBuilder.withValidator(NumberValidator.getNumberInstance()).withMinimum(1).withMaximum(1).create();
Option numOpt = oBuilder.withLongName("num").withArgument(numArg).create();
Group options = gBuilder.withOption(numOpt).create();

Then parsing --num -0.1 results in:

Unexpected -0.1 while processing --num