android/guava/src/com/google/common/collect/AbstractSetMultimap.java
@CanIgnoreReturnValue
  @Override
  public Set<V> removeAll(@NullableDecl Object key) {
    return (Set<V>) super.removeAll(key);
  }
@CanIgnoreReturnValue
  @Override
  public Set<V> removeAll(@NullableDecl Object key) {
    return (Set<V>) super.removeAll(key);
  }
{@inheritDoc}

<p>Because a {@code SetMultimap} has unique values for a given key, this method returns a
{@link Set}, instead of the {@link Collection} specified in the {@link Multimap} interface.