fn get(&self, l2_block_number: L2BlockNumber, hashed_key: H256) -> Option<StorageValue> {
        let lock = self.0.read().expect("values cache is poisoned");
        if lock.valid_for < l2_block_number {
            // The request is from the future; we cannot say which values in the cache remain valid,
            // so we don't return *any* cached values.
            return None;
        }

        let timestamped_value = lock.values.get(&hashed_key)?;
        if timestamped_value.loaded_at <= l2_block_number {
            Some(timestamped_value.value)
        } else {
            None // The value is from the future
        }
    }
Gets the cached value for `key` provided that the cache currently holds values
for `l2_block_number`.
core/lib/state/src/postgres/mod.rs