update method

V update (
  1. K key,
  2. V update(
    1. V value
    ),
  3. {V ifAbsent(
      )}
    )
    inherited

    This operation is not supported by an unmodifiable map.

    Implementation

    V update(K key, V update(V value), {V ifAbsent()}) {
  throw UnsupportedError("Cannot modify unmodifiable map");
}