The property mapping should return a value that is expected by the Provider/Source. What types are supported, is documented in the individual Provider/Source. Returning None is always accepted, this simply skips this mapping.
Context Variables
user: The current user, this might be None if there is no contextual user. (ref)
request: The current request, this might be None if there is no contextual request. (ref)
Arbitrary other arguments given by the provider, this is documented on the Provider/Source.