map<K, V> method
create FieldValidator for Map of key K
and value V
Implementation
FieldValidator<Map<K, V>?, Map<K, V>?> map<K, V>(
[String? Function(Map<K, V>? value)? validate]) {
return FieldValidator<Map<K, V>?, Map<K, V>?>._(
messages: _messages,
convert: (v) => v,
validate: (value) => validate?.call(value.value),
);
}