code: private static TerminalBindingCondition createWithCode(
              final String condition,
              final String message,
              final Integer code) {
          if (condition == null) {
              throw(new IllegalArgumentException(
                      "condition may not be null"));
          }
          if (message == null) {
              throw(new IllegalArgumentException(
                      "message may not be null"));
          }
          if (COND_TO_INSTANCE.get(condition) != null) {
              throw(new IllegalStateException(
                      "Multiple definitions of condition: " + condition));
          }
          TerminalBindingCondition result =
                  new TerminalBindingCondition(condition, message);
          COND_TO_INSTANCE.put(condition, result);
          if (code != null) {
              if (CODE_TO_INSTANCE.get(code) != null) {
                  throw(new IllegalStateException(
                          "Multiple definitions of code: " + code));
              }
              CODE_TO_INSTANCE.put(code, result);
          }
          return result;
      }
docs: Helper method to add entries.