ActivatedRoute.fragment was typed as Observable<string> but could emit
both null and undefined due to incorrect non-null assertion. These
non-null assertions have been removed and fragment has been retyped to
string | null.
BREAKING CHANGE:
Strict null checks will report on fragment potentially being null.
Migration path: add null check.
Fixes#23894, fixes#34197.
PR Close#37336
Matthias Kunnen
b5551609fe