dijit/Tree creates 'undefined' cookie by default

[Adam Peller]

Trees with persist:true (the default) but without an id or cookieName will persist state in a cookie called 'undefined'. This can be seen by simply running the themeTester. There are two trees, both persist their state. If you examine document.cookie you'll see

>>> document.cookie
"undefined=continentRoot; rootlessTreeSaveStateCookie=continentRoot"

[Adam Peller]

Not sure whether to recommend that the state not be persisted at all without an id, or whether a generated id should be used. The latter is questionable. If the entity is not named, it's probably not going to be used.

In retrospect (perhaps my bad) it probably would have also been better to use shorter names and have persist:false by default, since it's not hard to hit the HTTP 4k cookie limit with a couple of large open Tree widgets.

[bill]

I thought I fixed this in #12735. Guess I messed it up and should have been checking this.params.id not this.id, which can be auto-generated. (Although I don't know where that undefined is coming from, since as I said every Tree should have an auto-generated id.)

[bill]

In [28254]:

Don't try to save tree state if cookieName is undefined (which happens when there's no user specified id). Fixes #15088, refs #12735 !strict.