getPost() not working as expected

You should check for a POST request, and use the default values only for a GET request.

PHP Code:

if ($this->request->getMethod() === 'post') {
    $data['first_name'] = $this->request->getPost('first_name', FILTER_SANITIZE_STRING);
} else {
    $data['first_name'] = $data['employee_data']['first_name'];
} 


Many thanks,
I really appreciate your time and help.

So, I think we can conclude getPost() does not recognise empty form fields!