default MutableWorldState freezeStorage() {
    // no op
    throw new UnsupportedOperationException("cannot freeze");
  }
Persist accumulated changes to underlying storage.

@param blockHeader If persisting for an imported block, the block hash of the world state this
    represents. If this does not represent a forward transition from one block to the next
    `null` should be passed in.
ethereum/core/src/main/java/org/hyperledger/besu/ethereum/core/MutableWorldState.java