return new Object[0];
      }
      Map<K, V> delegate = delegateOrNull();
      return (delegate != null)
          ? delegate.keySet().toArray()
          : ObjectArrays.copyAsObjectArray(requireKeys(), 0, size);
    }

    @Override
    @SuppressWarnings("nullness") // b/192354773 in our checker affects toArray declarations
    public <T extends @Nullable Object> T[] toArray(T[] a) {