anchor.diff:  
   create_map(Json, #state{url = undefined}) ->
   	Url = "http://localhost:9093/map",
  -	Binary = jsx:to_json(Json),
  +	Binary = jsx:to_json(case Json of [] -> [{}]; _ -> Json end),
   	ibrowse:send_req(Url, [?cookie, ?accepts, ?contenttype], put, Binary).
   
   destroy_map(#state{url = Url}) ->
  
positive.code: 	true;
  precondition(_S, {call, _, create_map, _}) ->
  	false;
  precondition(#state{url = undefined}, Blorp) ->
  	false.
  
  %% =======================================================
  
negative.code: 	?LET(N,
  	list(
  		frequency([
  			{1, 9},
  			{8, integer(32, 126)},
  			{5, char()}
  		])
  	), unicode:characters_to_binary(N)).
  
  g_color() ->
  	oneof([
  