Godot Version
Four
Question
it keeps saying Attempt call function 'add_item' in a base 'null instance' on a null instance
Four
it keeps saying Attempt call function 'add_item' in a base 'null instance' on a null instance
Without code we can’t help u, but that means you’re trying to access a property/function in a null variable, a variable that contains nothing.
To add to what matheusmdx said, you will probably have a line like “something.add_item(…)” somewhere and the “something” part won’t have been set to anything (or will have been set to null). A code snippet would help people help you though.