Add Flavor to "Backspace" functionality

[TBenTiCon]

Hi there =)
following the Docs, i've greated my own Block Flavour and its working as expected. My Problem is, that it currently cant deleted.

Whenever i use "backspace" on it (like with the default blocks), im getting the following error:

chunk-CFKMG3VK.js?v=773be0fa:544 Uncaught Error: Failed to handle backspace! Unknown block flavours! flavour:question
    at handleUnknownBlockBackspace (chunk-CFKMG3VK.js?v=773be0fa:544:9)
    at handleParagraphDeleteActions (chunk-CFKMG3VK.js?v=773be0fa:436:153)
    at handleParagraphBlockBackspace (chunk-CFKMG3VK.js?v=773be0fa:448:21)
    at handleLineStartBackspace (chunk-CFKMG3VK.js?v=773be0fa:550:48)
    at onBackspace (chunk-6MXOMDQJ.js?v=773be0fa:47478:5)
    at Backspace (chunk-6MXOMDQJ.js?v=773be0fa:47752:12)
    at chunk-FMZVM7BV.js?v=773be0fa:898:19
    at chunk-FMZVM7BV.js?v=773be0fa:999:14
    at UIEventDispatcher.run (chunk-FMZVM7BV.js?v=773be0fa:1307:22)
    at KeyboardControl._down (chunk-FMZVM7BV.js?v=773be0fa:970:24)

How can i hook my custom block into the Backspace functionality?

BIG thank you for any help! =)