code: @Override
      public void validate(ValidationHelper helper, Context context, String key, ServerVariables t) {
          if (t != null) {
              boolean mapContainsInvalidKey = false;
              for (String k : t.keySet()) {
                  if (k == null || k.isEmpty()) {
                      mapContainsInvalidKey = true;
                  } else {
                      //Ensure map doesn't contain null value
                      if (t.get(k) == null) {
                          final String message = Tr.formatMessage(tc, "nullValueInMap", k);
                          helper.addValidationEvent(new ValidationEvent(ValidationEvent.Severity.ERROR, context.getLocation(), message));
                      }
                  }
              }
  
              //Ensure map doesn't contain an invalid key
              if (mapContainsInvalidKey) {
                  final String message = Tr.formatMessage(tc, "nullOrEmptyKeyInMap");
                  helper.addValidationEvent(new ValidationEvent(ValidationEvent.Severity.ERROR, context.getLocation(), message));
              }
          }
      }
docs: {@inheritDoc}