Error on Startup ('Assertion `script != __null' failed) - application unusable

[Tony Flury]

When starting grub-customizer, it builds the list of the current menu, and then generates a pop-up with the following error :

exception '15AssertException'
 with message 'Assertion `script != __null' failed. Function: _rAppendRule'
 in /build/buildd/grub-customizer-4.0.6/src/Controller/MainControllerImpl.cpp:391

In the terminal the following output is generated :

 *** initializing (w/o specified bootloader type)…
   * reading partition info…
   * Loading Framebuffer resolutions (background process)
   * Finding out if this is a live CD
sh: 1: hwinfo: not found
 *** initializing (w/ specified bootloader type)…
   * Checking if the config directory is clean
 *** loading configuration
 *** loading - preserveConfig: no
   * unsetting saved config
 *** loading settings
 *** loading grub list
   * loading scripts…
   * loading proxies…
   * cleaning up proxy configuration…
   * creating proxifiedScript links & chmodding other files…
   * running grub-mkconfig
   * restoring grub configuration
   * removing invalid proxies from list
     exception '28InvalidStringFormatException'
 with message 'unable to parse index from '
 in /build/buildd/grub-customizer-4.0.6/src/Model/Script.cpp:276
     exception '28InvalidStringFormatException'
 with message 'unable to parse index from '
 in /build/buildd/grub-customizer-4.0.6/src/Model/Script.cpp:276
     exception '28InvalidStringFormatException'
 with message 'unable to parse index from '
 in /build/buildd/grub-customizer-4.0.6/src/Model/Script.cpp:276
     exception '28InvalidStringFormatException'
 with message 'unable to parse index from '
 in /build/buildd/grub-customizer-4.0.6/src/Model/Script.cpp:276
     exception '28InvalidStringFormatException'
 with message 'unable to parse index from '
 in /build/buildd/grub-customizer-4.0.6/src/Model/Script.cpp:276
     exception '28InvalidStringFormatException'
 with message 'unable to parse index from '
 in /build/buildd/grub-customizer-4.0.6/src/Model/Script.cpp:276
     exception '28InvalidStringFormatException'
 with message 'unable to parse index from '
 in /build/buildd/grub-customizer-4.0.6/src/Model/Script.cpp:276
   * loading completed
 *** grub list completely loaded
 *** loading saved grub list