value of optional type 'String?' not unwrapped;did you mean to use '!'or '?'? : my code is below: 
@IBAction func registerButtonTapped(sender: AnyObject)
    {
        
        
        let userEmail = userEmailTextField.text;
        let userPassword = userPasswordTextField.text;
        let userConfirmPassword = confirmPasswordTextField.text;
        
        //check for empty fields
        if userEmail.isEmpty || userPassword.isEmpty || userConfirmPassword.isEmpty
        {
        //Display alert message
        
        displayMyAlertMessage("All fields are required");
        return ;
        
        }
