str-index should return null for a non-existent element rather than 0

[mirisuzanne]

Shouldn't both be false?

// input
.test {
  index: index(one two three, four);
  str-index: str-index('one two three', 'four');
}

// output
.test {
  index: false;
  str-index: 0;
}

[nex3]

Really it should return null, as per #832. I'll edit the issue title to reflect that.

It's a good thing you found this before 3.3 was released; it would be really hard to change this behavior later without breaking a bunch of people.

[xzyfer]

Just ran into this myself 👍