I prefer the Either option, and this is how all SEM interfaces are defined. After all if a user specifies the name of a particular output map she/he clearly wants it to be created. On the other hand if you don't want to be bothered with giving any specific names (and just want them to be generated by the interface) you can jsut set it to "True". I think this is more convenient and this is how we did stuff in many other interfaces.