The model/view split for the review request page broke checking for

updates to the review request. It still worked on the diff viewer, but

not on the review request updates page. The reason is that this page

does not provide a type of updates to check for, leaving it at the

default of null, which was not supported. Before the split, the

default would have been undefined, which was supported.
This change simply fixes the check, allowing any falsy values to be

considered valid to enable checking for all updates.

Made some updates to a review request. After a bit, the update bubble

showed up.