Used to indicate an uninitialized variable value. A variable value is uninitialized when it is first created and no value is assigned to it, or when a variable value is explicitly set to empty.
用于指明未初始化的变量值。

举例:
dim x   'x变量未初始化
x="ff"   'x已经不再是未初始化的变量了
x=empty   'x为初始化变量

Note: This is not the same as Null!!
注意：这和Null不同

Used to test if a variable is uninitialized.
用来测试变量是否为初始化

举例: If (isEmpty(x)) 'x是否为初始化变量？

举例: set myObject=nothing

举例: If (myObject Is Nothing) '它是否建立？

注意: If you compare a value to Nothing, you will not get the right result! Example: If (myObject = Nothing) 'always false!
如果你将值与Nothing做比较，将不会得到正确的结果！

One way to think of Null is that someone has explicitly set the value to "invalid", unlike Empty where the value is "not set".
对于“null”有一种解释方式为它被明确设置这个值为“无效”，而不像“Empty ”它的值为“not set”（没有被设定）

Note: This is not the same as Empty or Nothing!!
注意：null并不和Empty或 Nothing一样！

Example: x=Null 'x contains no valid data

Example: if (isNull(x)) 'is x invalid?