Locally, I observe:

 2:07.37     public void setWebNotificationDelegate(final @Nullable WebNotificationDelegate delegate) {
 2:07.37                 ^
 2:07.58 1 warning

How did that sneak past the new Javadoc lint? The answer is that it’s an “up-to-date” thing. The way that Gradle works, it doesn’t actually re-run the Javadoc task, so the warning doesn’t show up if it's shown up in a previous task (build, say). That's what's happening, I think, in the A(lints) job where this landed: https://treeherder.mozilla.org/#/jobs?repo=autoland&revision=2d59ce318c46327d78c46c00086ea847223c383c&selectedJob=262768326.

To address this, I reckon that we need to do one of the following, in rough descending order of preference:

1. Ensure that the JSON output file is a task output, and ensure that it's not in the objdir before we run the lint, so that the task must run to create it
2. Split the Gradle tasks in some way so that Javadoc always runs
3. Force the Javadoc task to always run (and accept slower local builds)

https://hg.mozilla.org/mozilla-central/rev/0f5a98fe7608