In certain (unknown) cases, a service worker registration object may return a null serviceworker in installing state, right after calling update() on the service worker registration object.

The below initialization code (shared by many flutter web apps) is affected:

• flutter/dev/integration_tests/web/web/index.html

  Lines 56 to 62 in b87caba

  	} else if (!reg.active.scriptURL.endsWith(serviceWorkerVersion)) {
  	// When the app updates the serviceWorkerVersion changes, so we
  	// need to ask the service worker to update.
  	console.log('New service worker available.');
  	reg.update();
  	waitForActivation(reg.installing);
  	} else {

(reg.installing is null, when it shouldn't.)

Steps to Reproduce

@yjbanov managed to get his Chrome browser (v100, gLinux) in this state and immediately reported the issue, but I couldn't repro. The only way we've had to reproduce the issue was to eliminate forking in the code at this point, and force the code through that specific branch.

Expected results: An app running

Actual results: A variation of this error: