The first half of this method has a supposition that $args is not empty. Just put all of it inside if ($subCommand !== null) condition. Refactor the remainder of the first half of the method accordingly by getting rid of unnecessary checks against null-pointer.

If $subCommand is null, the second half of the method kicks in.

In a nutshell, this method checks against subcommands, if any exist, responds to them. Otherwise it responds to the main listener (afai understand).

As you are at it, please also fix L257: It's ridiculous to check against one variable and prepend another even though their values are the same.

Honestly, I would only do more than the bare minimum if this whole component got extracted and stopped being seen de facto deprecated.