cannot detect empty content when I use backspace

[sagho0or]

hello :)
I have a problem on validation form when I use ngx-quill-editor.
content is a require field in my form. but unfortunatly when I write content and set it rtl, then I delete it (clean whit Ctrl+A and ba, ngModel get this :

I expect it will be clean if I delete content. how can I check this field is filled or not on submit?