I can't stand the way VBScript handles non-values.  Consider the following:

This fails unless your SomeFunction() function specifically returns an empty string, such as:

This is because even an empty string is considered a value in VBScript, on which you can check the length and check for IsEmpty().  However, this doesn't work if your function returns a variable that has no value, like this:

In this case, if the SomeOtherFunction() did not return a value, then the value of strValue is NULL.  In VBScript, a NULL is defined as "no valid data."  So, the only way to validate this variable is to check for NULL:

Because strValue does not hold valid data, IsNull() evaluates to TRUE.  Now, in the case of objects, where you expect a function to return an object, you have to use a completely different method:

Strange, and not entirely intuitive, but there it is...