Standardize getter return values for empty sets.

[cowboy]

Just like getter-setter detection logic has been standardized on arguments, it might be a good idea for empty-set getters to always return a consistent value. I vote for null.

I also understand if .text() must continue to behave differently, because it's already a special case in other ways, and we need something to laugh at ironically.

$.fn.jquery   // "1.7.2"
$().attr("x") // undefined
$().prop("x") // undefined
$().css("x")  // undefined
$().val()     // undefined
$().text()    // ""
$().html()    // null
$().offset()  // null

Please don't do this in a patch release, though! <3 (zing)

[dmethvin]

I'd prefer undefined since that changes fewer cases and avoids the Object-ness of null. Neither .html nor .offset have documented returns for empty sets so it should be safe to change. No way we're messing with .text buddy. :)

[Uri Gilad]

Fix #11962. Standardize getter return values for empty sets.

Changeset: 21b0db7993315f0a5390798fefe63eb21891493e