* CollectionRemoveTester.testRemove_nullAllowed, but it's not clear that it's
   * a good policy, especially because, in order for the test to pass, the
   * parameter must be misleadingly annotated as @Nullable. I suspect that
   * we'll want to remove @Nullable, add an eager checkNotNull, and loosen up
   * testRemove_nullAllowed.
   */
  @CanIgnoreReturnValue
  @Override