Function adds_field 

pub fn adds_field<'a>(
    schema: &ClassSchema,
    class_exists: bool,
    keys: impl IntoIterator<Item = &'a str>,
    is_delete: impl Fn(&str) -> bool,
) -> bool

canAddField (DatabaseController.js:970-998): does this write introduce a field the schema does not have?

class_exists is upstream’s if (!classSchema) return, so a write that creates the class never runs the addField gate at all.