anchor.diff:  
   resource_exists(ReqData, Ctx) ->
       wallaroo_web_common:generic_entity_exists(ReqData, Ctx, fun(Name, Commit) -> 
  -								    Res = wallaroo:get_entity(Name, group, Commit),
  -								    % error_logger:warning_msg("looking for group ~p; got ~p~n", [Name, Res]),
  -								    Res
  +								    ?D_VAL(wallaroo:get_entity(Name, group, Commit)),
   							    end).
   
   content_types_accepted(ReqData, Ctx) ->
  
positive.code: -export([allowed_methods/2, content_types_provided/2, content_types_accepted/2, finish_request/2]).
  
  -include_lib("webmachine/include/webmachine.hrl").
  
  init(Args) ->
      wallaroo_web_common:generic_init(Args).
  
negative.code: 
  %%% XXX: this doesn't do proactive graph validation yet -- but it could (and should)
  validate({wallaby_group, _}=Group, none) ->
      ?D_LOG("validating ~p for no commit~n", [Group]),
      Features = {nonexistent_features, wallaby_group:features(Group)},
      Parameters = {nonexistent_parameters, [P || {P, _} <- wallaby_group:parameters(Group)]},
      case [Fail || Fail={_, Ls} <- [Features, Parameters], Ls =/= []] of
  