As GNUstep is a Free Software Foundation project, contributed code needs to have its copyright assigned to the Free Software Foundation.
This is so that, if someone tries to take that code, modify it, and use it in a proprietary product without allowing other people (such at the author of the code) to use the modifications, the FSF is able to use copyright law to force them to make the modifications public.
A common paranoid misconception (i.e. FUD spread by anti-FSF people) is that assigning copyright to the FSF means that the FSF can then take the code you wrote away from you and stop you using it. In fact their practice is to assign back rights for you to do whatever you like with the code you wrote (including using it in proprietary projects).
Please contact the GNUstep maintainer for details about copyright assignment.