Empty field at login

-- url of the page with the problem -- : www.telchines.gr/
-- HikaShop version -- : 2.5.0
-- Joomla version -- : 3.4.4

Hello!
If someone wants to login to buy a product, there are two fields to fill in: 1) email and 2) password.
Now, if i write my email but leave the password field empty, the page loads to the next step of the checkout progress.
For example: [url=http://http://www.telchines.gr/el/top-sellers/checkout]http://www.telchines.gr/el/top-sellers/checkout[/url]
Try to login without writting a password to see what i mean.
Is there any way to have a popup message in that case?

Thank you in advance

www.telchines.gr/index.php?option=com_hi...y_pathway=24&lang=el

click the red button "Προσθήκη στο καλάθι"
and then click the red button at the top right corner "Ολοκλήρωση παραγγελίας"
After that you will go automatically at the checkout page which requires login or register if you want to shop.
Once you are there, try to login like i mentioned previously.

Thank you!

No, please do the opposite. Blanc email and a random password. I found this public_html/plugins/authentication/joomla/joomla.php
======

public function onUserAuthenticate($credentials, $options, &$response)
{
$response->type = 'Joomla';

// Joomla does not like blank passwords
if (empty($credentials))
{
$response->status = JAuthentication::STATUS_FAILURE;
$response->error_message = JText::_('JGLOBAL_AUTH_EMPTY_PASS_NOT_ALLOWED');

return;
}
================
from line 32 to 41 that does the job for blanc email.

I tried to change the code there and add the 'password' somehow but , I didnt make it.
Joomla bug I believe but I would really appriciate it if you could paste the correct code.

Can I do something like that to make that condition work for username also?

public function onUserAuthenticate($credentials, $options, &$response)
	{
		$response->type = 'Joomla';

		// Joomla does not like blank passwords
		if (empty($credentials['password','username']))
		{
			$response->status        = JAuthentication::STATUS_FAILURE;
			$response->error_message = JText::_('JGLOBAL_AUTH_EMPTY_PASS_NOT_ALLOWED');

			return;
	}

thanks for the code nikolas!
Unfortunately it doesn t stop to empty username. If you can give it a try...

I have in
public_html/plugins/authentication/joomla/joomla.php

public function onUserAuthenticate($credentials, $options, &$response)
	{
		$response->type = 'Joomla';

		// Joomla does not like blank passwords
                if (empty($credentials['password']) || empty($credentials['username']))
		{
			$response->status        = JAuthentication::STATUS_FAILURE;
			$response->error_message = JText::_('JGLOBAL_AUTH_EMPTY_PASS_NOT_ALLOWED');

			return;
		}

Hi Nicolas!
It did work, just one detail that needs to be fixed, the message is correct but it appears as a success message with green background and letters. Also when the message pops, it's not on the step 0 of the checkout progress, so as result i have to click the button "Επόμενο" to go back to login.
I m sending screenshots to see.

Thank you