[Supports] Cannot Change PHP version via Plesk Panel

On Plesk 12.5.x, when change your site's PHP version to something else other than the vendor OS, you may got error:

ERROR: Call to a member function getValue() on null (PhpSettings.php:105)

This is because of the PHP handlers not enable or the version you are selected not well install in Plesk so follow the Plesk Support states as following:

1. Disable all 3rd-party repositories.
   
2. Reinstall the PHP versions using Plesk autoinstaller.
   
3. Enable all PHP handlers on Tools & Settings > PHP Settings page.
   

   

   Tools & Setting > PHP Settings

   
   
   

   

   e.g. PHP 7 CGI, FPM and FastCGI to be able to switch to it

   
   
4. Update information about all PHP handlers settings
   

   ~# plesk bin php_handler --reread