(using GMS 1, so if youre using 2 idk if this will help)
hey! i think i finally figured this one out, though its not a complete solution it looks like. its in the create_dialogue script, down in the switch(arg_count-1) statement.
at the end of each case youll see an if statement that checks if(a[i] != 0) . i added && !is_undefined(a[i]) to each one, and from a quick test it looks like that worked, at least in the base project.
since the text events use a different script than the normal dialogue, however, those are still broken.