In some cases, we'd get the following error:

"string sub-command REGEX, mode MATCH needs at least 5 arguments total to
command."

This fix overcomes that issue. I suspect the "output" was empty on these setups
and that'd cause the command to fail. This ensures that the empty string is
recognized correctly as an argument.

Change-Id: If539c4f169602bb4fd9a00242b02badf2d7e82e4