*<Null safety>*
CanonicalizedMap<C, K, V>.from(Map<K, V> other, C canonicalize(K key), {bool isValidKey(K key)})
CanonicalizedMap.from(Map<K, V> other, C Function(K key) canonicalize, {bool Function(K key)? isValidKey}) : _canonicalize = canonicalize, _isValidKeyFn = isValidKey { addAll(other); }