Fix NullPointerException in TextUtil.compare

[OnkelDok]

https://forum.portfolio-performance.info/t/fehlermeldung-internal-error/32110

I dont know why, but it seems at least one security name is null. So I added a global fix for all users of TextUtil.compare and also created simple unittest.

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One additional point I thought about: In the code there are plenty of this nullchecks for comparisons (e.g. https://github.com/portfolio-performance/portfolio/blob/master/name.abuchen.portfolio/src/name/abuchen/portfolio/model/Security.java#L53-L58).
Would it be helpful/better to create a commonly used method where this nullcheckss are executed and use this everywhere?
Of course this is only possible by using Optional to also realize the path when both objects/values are not null.
Does that make sense?

[Nirus2000]

Hello @OnkelDok
Awesome thing from once again... 😲
I read your entry and think about it for a moment and then the aha! moment... 👀
Maybe the change fits better... take a look at it at your leisure.

Geil 👍🏻

Regards
Alex

[Nirus2000]

Suggested change

	if (left == null && right == null)
	return 0;
	else if (left == null)
	return -1;
	else if (right == null)
	return 1;
	if (left == right) return 0; // Both are null or refer to the same object
	if (left == null) return -1;
	if (right == null) return 1;

[Nirus2000]

Suggested change

	assertEquals(-1, TextUtil.compare(null, "a"));
	assertEquals(1, TextUtil.compare("a", null));
	assertEquals(0, TextUtil.compare(null, null));
	assertEquals(-1, TextUtil.compare(null, "a"));
	assertEquals(1, TextUtil.compare("a", null));
	assertEquals(0, TextUtil.compare(null, null));
	assertEquals(0, TextUtil.compare("abc", "abc"));
	assertTrue(TextUtil.compare("a", "b") < 0); // "a" should be less than "b"
	assertTrue(TextUtil.compare("z", "y") > 0); // "z" should be greater than "y"
	assertTrue(TextUtil.compare("abc", "ABC") != 0); // Depends on COLLATOR
	assertTrue(TextUtil.compare("café", "cafe") != 0); // Accents matter

[OnkelDok]

Interesting idea. I don't thought about it before. Maybe for strings this is fine. But I think I want only check for null and let the underlaying comparer make the decision for not-null objects.
It's up to @buchen what to use.