When I save data skip the validation for associated field?

Users Table
Email(username)

validation Rules in Users Model->

    	$validator
            ->requirePresence('username')
            ->add('username', 'validFormat', ['rule' => 'email', 'message' => 'Email id must be valid'])
            ->maxLength('username', 150)
            ->allowEmptyString('username', false, 'Please enter your email id');

validation Rules in Employee Model->

	 	$validator->allowEmptyString('username');

email(Username) saved in User table when user in Employee add data.
when I save employee data i want skip the validation for usernames
i tried following code but it won’t works.

$employee = $this->Employees->patchEntity($employee, $this->request->getData(), [‘validate’ => false]);

any suggestion