How to validate an input field if value is not null in Laravel

In case column is nullable

'password' => 'nullable|min:6|confirmed',

@Rejinderi's answer is correct!

In case column is not nullable (This may help other)

'password' => 'sometimes|required|min:6|confirmed',

Result

username = 'admin',
password = null // fail- required

username = 'admin',
password = 123 // fail- min:6

username = 'admin' // pass- validate only exist

try using nullable as a rule

'password' => 'nullable|min:6|confirmed',

see https://laravel.com/docs/5.8/validation#a-note-on-optional-fields