Checks whether the given value is null or not declared.
A value is null if:
If one of the conditions is fulfilled, isnull() returns true, otherwise false.
- it is a variable or object (field) and is not declared
- it is the null value.
| input:||resulting output:|
<let D=null; ? isnull(D)>
<let D=null; ? isdecl(D)>
<let D=null; ? isempty(D)>
<? isnull(" ")>
<? isempty(" ")>
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.
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