private static @Nullable PsiElement getExpression(@NotNull PsiElement element) {
      if (element instanceof PsiAssignmentExpression) {
        PsiExpression target = PsiUtil.skipParenthesizedExprDown(((PsiAssignmentExpression)element).getLExpression());
        return ObjectUtils.tryCast(target, PsiReferenceExpression.class);
      }
      if (element instanceof PsiUnaryExpression) {
        PsiExpression target = PsiUtil.skipParenthesizedExprDown(((PsiUnaryExpression)element).getOperand());
        return ObjectUtils.tryCast(target, PsiReferenceExpression.class);
      }
      if (element instanceof PsiDeclarationStatement) {
        //should not happen
        return element;
      }
      return null;
    }
private static @Nullable PsiElement getExpression(@NotNull PsiElement element)