code: public ChangesetInfo subscribe(long id)
  	{
  		SingleElementHandler<ChangesetInfo> handler = new SingleElementHandler<>();
  		ChangesetInfo result;
  		try
  		{
  			String apiCall = CHANGESET + "/" + id + "/subscribe";
  			osm.makeAuthenticatedRequest(apiCall, "POST", new ChangesetParser(handler));
  			result = handler.get();
  		}
  		catch(OsmConflictException ignore)
  		{
  			/* ignore this exception which occurs when the user already subscribed to the changeset */
  			result = get(id);
  		}
  		return result;
  	}
docs: Subscribe the user to a changeset discussion. The changeset must be closed already.
  
  @param id id of the changeset
  @return the changeset
  
  @throws OsmAuthorizationException if this application is not authorized to modify the map
  (Permission.MODIFY_MAP)
  @throws OsmNotFoundException if the given changeset does not exist