docs: private static QName variableTypeRefOrErrIfNull(DMNModelImpl model, InformationItem variable) {
          if ( variable.getTypeRef() != null ) {
              return variable.getTypeRef();
          } else {
              MsgUtil.reportMessage( logger,
                      DMNMessage.Severity.ERROR,
                      variable,
                      model,
                      null,
                      null,
                      Msg.MISSING_TYPEREF_FOR_VARIABLE,
                      variable.getName(),
                      variable.getParentDRDElement().getIdentifierString() );
              return null;
          }
      }