code: def append_diff_hist(diff, diff_hist=list()):
      
      diff, diff_hist = _norm_json_params(diff, diff_hist)
  
      if not diff_hist:
          diff_hist = list()
  
      diff_hist.append({'diff': diff, 'diff_date': now_field()})
      return diff_hist
docs: Given a diff as generated by record_diff, append a diff record to the
      list of diff_hist records.