Constant RESTORED_MISSING_SLOT_CLASS 

pub const RESTORED_MISSING_SLOT_CLASS: &str = "miniextendr_restored_missing_slot";

The class of the error a rebuild hook gets when it reads a Sidecar field the save has no slot for: a field added after the version that saved the object (#2187). The condition carries field, the field’s name. The try_<field> getters return None instead.