isnull

Purpose: Checks whether the given value is null or not declared.

Return Values: A value is null if:

• it is a variable or object (field) and is not declared
• it is the null value.

Example:

input:	resulting output:
<? isnull(null)>	true
<? isnull(U)>	true
<? isdecl(U)>	false
<? isempty(U)>	true
<let D=null; ? isnull(D)>	true
<let D=null; ? isdecl(D)>	true
<let D=null; ? isempty(D)>	true
<? isnull(" ")>	false
<? isempty(" ")>	true

Tip: If it's not obvious how to use this function, imagine that you have a variable named D that has been declared, but has been assigned a null value and another variable U that has not been declared. In contrast to the isdecl() function, isnull() would return true for both variables.

See Also: isdecl(), isempty().