Ok, "leader" is a usable name. However, as you said, when you try to access the variable "leader", OFP looks for the command leader instead. Since you can do the same thing with "null", but OFP doesn't look for the command null, it still means that null is not a command, and is not different from any other random text. "dsdfsf" seems to produce the same effect that "null" has.
Thanks,
Bluelikeu