required method
Below are base case validatior functions, they are provided to cover most basic use cases that might be encountered.
They use the validation functions from StraingValidationFunctions to complete the actual validation
Adds StraingValidationFunctions.required to the function validation chain
Implementation
/// Adds [StraingValidationFunctions.required] to the function validation chain
FormValidator required({String? nullError, String? emptyError}) {
return _chain((String? s) => StraingValidationFunctions.required(s,
nullErrorMessage: nullError, emptyErrorMessage: emptyError));
}