Compose multiple validators into a single function that returns the union of the individual error maps.
Source
static ValidatorFn compose(List<ValidatorFn> validators) {
if (validators == null) return null;
var presentValidators = validators.where((v) => v != null).toList();
if (presentValidators.length == 0) return null;
return (model_module.AbstractControl control) {
return _mergeErrors(_executeValidators(control, presentValidators));
};
}