How to render json with objects from mongodb?

Question

Erlang

There is this code:

index('GET', []) ->
  Users = boss_db:find(consumer, []),
  {json, [{"users", Users}]}.

It doesn't work, it says:

{function_clause,
    [{boss_json,json_data1,
         [[{consumer,"consumer-52a3024b4346e12118000001",<<"qwe">>,
               <<"qwe">>},
           {consumer,"consumer-52a302c84346e12118000002",<<"asd">>,
               <<"asd">>},
           {consumer,"consumer-52a305264346e12118000003",<<"zxc">>,
               <<"zxc">>}],
          ["user"],
          []],
         [{file,"src/boss/boss_json.erl"},{line,23}]}

What to do with it? How to convert an array of objects so that it is rendered in json?