"Add new group" button not working – My Solution

I read this topic – https://www.ads-software.com/support/topic/add-new-group-button-not-working?replies=12
But don’t find solution for version 0.36.

My solution:

Open class-woocommerce-price-by-country-settings.php
Find: (line 140)
echo '<option value="' . $k . '"' . $selected . '>' . $v . '</option>\ ';

Change to:
echo '<option value="' . htmlspecialchars($k, ENT_QUOTES) . '"' . $selected . '>' . htmlspecialchars($v, ENT_QUOTES) . '</option>\ ';

Find: (line 205)
html1 += '<option value="<?php echo $k ;?>" '+selected+'><?php echo $v ?></option>\ ';

Change to:
html1 += '<option value="<?php echo htmlspecialchars($k, ENT_QUOTES) ;?>" '+selected+'><?php echo htmlspecialchars($v, ENT_QUOTES) ?></option>\ ';

https://www.ads-software.com/plugins/woocomerce-price-by-country/