null string

基本解釋

The CLP recognizes 'NULL' (specified in uppercase characters) as a null string. For example
CLP 將“NULL”（以大寫字符指定）識別為空字符串。
If a page action method invocation returns a non-null string value, Seam treats it as a navigation event.
如果頁面動作方法調(diào)用返回一個非空字符串值，則 Seam 將其當作一個導航事件。
The default namespace is initialized to be no namespace-URI at all, so there is a syntax for undefining a previously-defined default namespace by assigning it to the null string.
對缺省名稱空間初始化，使之完全不是名稱空間 URI，這樣就存在一個語法，它通過向以前定義的缺省名稱空間分配空字符串來取消對該名稱空間的定義。

NULL If a get string returns null, that pretty much means something went wrong and there are a few things that could go wrong.
如果GetSting返回，大致上表示的是出錯了,這里有幾種出錯的地方。
哈佛公開課 - 計算機科學課程節(jié)選