validate method
void
validate()
Validation method to ensure required fields are present
Implementation
void validate() {
if (to.isEmpty) {
throw StateError('Mailable must have at least one recipient in "to"');
}
if (subject.isEmpty) {
throw StateError('Mailable must have a non-empty subject');
}
if (view.isEmpty) {
throw StateError('Mailable must have a view path');
}
}