code: public void addMembership(Membership membership) throws RedmineException {
  		final Project project = membership.getProject();
  		if (project == null)
  			throw new IllegalArgumentException("Project must be set");
  		if (membership.getUser() == null)
  			throw new IllegalArgumentException("User must be set");
  		transport.addChildEntry(Project.class, getProjectKey(project),
  				membership);
  	}
docs: Add a membership.
  
  @param membership
  membership.
  @throws RedmineException