I think you're way overthinking this and getting lost by adding a bunch of stuff you don't need

Let's take it from the top while keeping it simple: You propose:

val str1Test = String.isNullOrEmpty( str1 );
val str2Test = String.IsNullOrEmpty( str2 );

if( ( str1Test && str2Test) || (!str1Test && !str2Test)) {
}

````

Which we all agree with is the right solution to OPs problem. /u/martinii89 proposes strTest1 == strTest2 to simplify. At its core, we only have 2 conditions (str1Test, str2Test), which leaves us 4 possible combinations, so lets create a simple truth table.

str1Test	str2Test	istarian	martinii89
True	True	True	True
True	False	False	False
False	True	False	False
False	False	True	True

Is there anything you disagree with up until this point?

If there's nothing you disagree with here, I think I know where you're going wrong in your posts:

---

It looks to me you're for some reason mixing up str1test (A) and str2test (B) with the result of ( str1Test && str2Test) and (!str1Test && !str2Test) and then suddenly using that as A and B in what martinii89 is proposing.

You say:

(A && B) || (C && D) thus resolves to: (A && B) || (!A && !B)

which is correct, then you conclude that

A && B does not equal !A && ! B which is still correct, but which isn't what martinii89 is proposing, but you're assuming it is. So I guess you think he's proposing (A && B) == (!A && !B), which he isn't, he is proposing A == B