anchor.diff:  
   -record(stats, {
   	file  :: atom(),
  -	line  :: non_neg_integer(),
  +	line  :: non_neg_integer() | 'undefined',
   	tries :: non_neg_integer(),
   	colls :: non_neg_integer(),
   	time  :: non_neg_integer(), % us
   	nt    :: non_neg_integer(), % #timings collected
  -	hist  :: tuple()            % histogram
  +	hist  :: tuple() | 'undefined'  % histogram
       }).
   
   -record(lock, {
  
positive.code: %%
  %% %CopyrightBegin%
  %%
  %% Copyright Ericsson AB 2010-2013. All Rights Reserved.
  %%
  %% Licensed under the Apache License, Version 2.0 (the "License");
  %% you may not use this file except in compliance with the License.
  
negative.code: 
  stats2stats([]) -> [];
  stats2stats([Stat|Stats]) ->
      Sz = record_info(size, stats),
      [stat2stat(Stat,Sz)|stats2stats(Stats)].
  
  stat2stat(Stat,Sz) when tuple_size(Stat) =:= Sz -> Stat;
  