docs: def set_source(self, source_id):
          """Sets the source.
  
          arg:    source_id (osid.id.Id): the new publisher
          raise:  InvalidArgument - ``source_id`` is invalid
          raise:  NoAccess - ``Metadata.isReadOnly()`` is ``true``
          raise:  NullArgument - ``source_id`` is ``null``
          *compliance: mandatory -- This method must be implemented.*
  
          """
          # Implemented from template for osid.resource.ResourceForm.set_avatar_template
          if self.get_source_metadata().is_read_only():
              raise errors.NoAccess()
          if not self._is_valid_id(source_id):
              raise errors.InvalidArgument()
          self._my_map['sourceId'] = str(source_id)