protected @Nullable String getExpressionBound(@NotNull PsiExpression expr) {
    PsiType type = expr.getType();
    if (isNumber(type)) {
      return expr.getText();
    }
    else if (isArray(type)) {
      return expr.getText() + ".length";
    }
    else if (isIterable(type)) {
      return expr.getText() + ".size()";
    }
    return null;
  }
protected @Nullable String getExpressionBound(@NotNull PsiExpression expr)