fn is_write_initial(&mut self, key: &StorageKey) -> bool {
        if let Some(&is_write_initial) = self.cache.initial_writes.get(key) {
            is_write_initial
        } else {
            let is_write_initial = self.storage_handle.is_write_initial(key);
            self.cache.initial_writes.insert(*key, is_write_initial);
            is_write_initial
        }
    }
Only keys contained in the underlying storage will return `false`. If a key was
inserted using [`Self::set_value()`], it will still return `true`.
core/lib/vm_interface/src/storage/view.rs