Add nullability annotations for static utils in java.util.

This change annotates Arrays, Collections, and Objects.

The most interesting decision here is probably annotating the Object
argument of the various Objects.requireNonNull overloads. Under the
normal rules, this would be @NonNull, because the method throws NPE if
it's null. This change annotates them as @Nullable because throwing
NPE on null is the whole point of the method, and calling it with an
argument which is provably non-null is pointless; or, to put it
another way, the method exists to convert possibly-@Nullable T to
definitely-@NonNull T with an exception thrown in a controlled
fashion.

Note that the methods involving natural sort ordering of arrays or
collections require the elements to be non-null, because they end up
calling e1.compareTo(e2) for arbitrary pairs of elements. For the
methods that take Comparators, the nullability of the elements match
the parameter of the Comparator's type parameter.

Test: make core-current-stubs-nullability-validation-check-nullability-warnings
Bug: 64930165
Change-Id: I52744d72da857751274fe44f58cff38e6d6b8a2f

0 files changed, 0 insertions, 0 deletions