code: @Override
      public String toTraceableView() {
          final String baseView = super.toTraceableView();
          final StringBuilder sb = new StringBuilder();
          sb.append(baseView); // same as toString()
          if (checkingOutRequestPath != null) {
              sb.append("\n latest checkOut(): ").append(checkingOutRequestPath).append(", ");
              sb.append(checkingOutEntryExp).append(", ").append(checkingOutUserExp).append(", ").append(checkingOutMillis);
          }
          if (checkingInRequestPath != null) {
              sb.append("\n latest checkIn(): ").append(checkingInRequestPath).append(", ");
              sb.append(checkingInEntryExp).append(", ").append(checkingInUserExp).append(", ").append(checkingInMillis);
          }
          if (closingReallyRequestPath != null) {
              sb.append("\n closeReally(): ").append(closingReallyRequestPath).append(", ");
              sb.append(closingReallyEntryExp).append(", ").append(closingReallyUserExp).append(", ").append(closingReallyMillis);
          }
          return sb.toString();
      }
docs: --------------