code: public CMASpaceMembership create(String spaceId, CMASpaceMembership membership) {
      assertNotNull(spaceId, "spaceId");
      assertNotNull(membership, "membership");
  
      final CMASystem sys = membership.getSystem();
      membership.setSystem(null);
  
      try {
        return service.create(spaceId, membership).blockingFirst();
      } finally {
        membership.setSystem(sys);
      }
    }
docs: Create a new membership.
  <p>
  This method will override the configuration specified through
  {@link CMAClient.Builder#setSpaceId(String)} and will ignore
  {@link CMAClient.Builder#setEnvironmentId(String)}.
  
  @param spaceId    the space id to host the membership.
  @param membership the new membership to be created.
  @return the newly created membership.
  @throws IllegalArgumentException if space id is null.
  @throws IllegalArgumentException if membership is null.