Needs a 'nullable' rule

[shrimpwagon]

This is very useful especially for dates. Where it is optional and can be null but can also be a valid date.

Look up Laravel's validation rules. They have it too and it explains more.

[willemwollebrants]

We have it, but it's called 'optional':

From the readme
optional - Value does not need to be included in data array. If it is however, it must pass validation.

$validator = new \Valitron\Validator();
$validator->rule('optional', 'date');
$validator->rule('date', 'some_date');
//field not set
$validator->validate(); //true
//field is null
$validator->withData(['some_date'=>null])->validate(); //true
//value is valid
$validator->withData(['some_date'=>'2020-02-21'])->validate(); //true
//value is not valid
$validator->withData(['some_date'=>'not a date'])->validate(); //false