Handle falsy values in addHelpCommand() properly

[aweebit]

Cherry-picked from #1926 for better separation of concerns.

Problem

Only false is treated as falsy in addHelpCommand().

ChangeLog

Fixed

• falsy parameter value handling in .addHelpCommand()

[shadowspawn]

The false check is as intended.

(I would normally leave this open for discussion, but you are have opened ~15 Pull Requests in the last week with ~160 comments between us. I don't have the time to continue that level of feedback.)