Backspace key error

[avoinea]

How to reproduce:

• Go to a slate block at the end
• Type Enter
• Type something
• Use the Backspace key to delete text until the block is removed
• Sometimes you get this error

https://user-images.githubusercontent.com/323385/143418836-81c109d9-ab42-491a-8e34-57bf91f2bd49.mp4

[nileshgulia1]

I think this is solved in #195