addAll method
inherited
Adds all associations of other to this multimap.
The operation is equivalent to doing this[key] = value for each key and
associated value in other. It iterates over other, which must therefore
not change during the iteration.
This implementation iterates through each key of other and adds the
associated values to this instance via addValues.
Implementation
void addAll(Multimap<K, V> other) => other.forEachKey(addValues);