anchor.diff:      R3 = [#{name => Name,
               resolution => Resolution,
               values => mmath_bin:to_list(Data),
  -            metadata => Mdata,
  +            metadata => maps:map(fun to_null/2, Mdata),
               type => <<"metrics">>}
             || #{name := Name,
                  data := Data,
  
positive.code:                metadata := Mdata,
                 resolution := Resolution} <- R2],
      R4 = [#{name => Name,
              metadata => Mdata,
              values => [#{timestamp => Ts, event => E}
                         || {Ts, E} <- Data],
              type => <<"events">>}
  
negative.code:         _ ->
              D
      end.
  
  to_null(_, undefined) ->
      null;
  to_null(_, V) ->
      V.
  
  content_type(Req) ->
      {ok, A, Req1} = cowboy_req:parse_header(<<"accept">>, Req),
  