anchor.diff:  
   start_mappers([], _QTerm, Accum, FsmKeys) ->
       {Accum, FsmKeys};
  -%% TODO Figure out why we're getting zero-key partitions
  -%%      from the planner. We shouldn't need this clause, IMHO.
  -start_mappers([{_Partition, []}|T], QTerm, Accum, FsmKeys) ->
  -    start_mappers(T, QTerm, Accum, FsmKeys);
   start_mappers([{Partition, Inputs}|T], QTerm, Accum, FsmKeys) ->
       case riak_kv_map_master:new_mapper(Partition, QTerm, Inputs, self()) of
           {ok, FSM} ->
  -            %%log_event(start_mapper, [FSM]),
               Accum1 = dict:store(FSM, length(Inputs), Accum),
               start_mappers(T, QTerm, Accum1, FsmKeys ++ [{FSM, [{keys, {Partition, Inputs}}]}]);
           Error ->
  
positive.code: 
  handle_event({register_mapper, Id, MapperPid}, #state{mapper_data=MapperData}=State) ->
      MapperData0 = case lists:keyfind(Id, 1, MapperData) of
          {Id, MapperProps} -> lists:keyreplace(Id, 1, MapperData, {Id, MapperProps ++ [{pid, MapperPid}]});
          false -> MapperData
      end,
      MapperData1 = MapperData0 ++ [{MapperPid, Id}],
  
negative.code:             end;
          false -> throw(bad_mapper_props_no_id)
      end.
  