anchor.diff:    case bson:lookup(<<"_id">>, Doc) of
       {} -> bson:update(<<"_id">>, mongo_id_server:object_id(), Doc);
       _Value -> Doc
  -  end.
  +  end.
positive.code: 
  
  %% @private
  %% Convert maps or proplists to bson
  prepare_doc(Docs, AssignFun) when is_list(Docs) ->  %list of documents
    case mc_utils:is_proplist(Docs) of
  
negative.code: 
  
  -type cursorid() :: integer().
  -type selector() :: map().
  -type projector() :: bson:document() | map().
  -type skip() :: integer().
  -type batchsize() :: integer(). % 0 = default batch size. negative closes cursor
  