@Override
      public void visitReferenceExpression(@NotNull PsiReferenceExpression expression) {
        final PsiElement element = expression.resolve();
        if (element instanceof PsiVariable) {
          result.add((PsiVariable)element);
        }
        final PsiExpression qualifier = expression.getQualifierExpression();
        if (qualifier != null) {
          qualifier.accept(this);
        }
      }
@Override
      public void visitReferenceExpression(@NotNull PsiReferenceExpression expression)