public Optional<UInt256> getKey() {
    return key;
  }
The original key used for this storage entry. The hash of this key is used to store the value
in the storage trie, so a preimage of the trie key must be available in order to provide the
original key value.

@return If available, returns the original key corresponding to this storage entry.
evm/src/main/java/org/hyperledger/besu/evm/account/AccountStorageEntry.java