@Override
  public MutableAccount createAccount(final Address address, final long nonce, final Wei balance) {
    if (getAccount(address) != null) {
      throw new IllegalStateException("Cannot create an account when one already exists");
    }
    SimpleAccount account = new SimpleAccount(address, nonce, balance);
    accounts.put(address, Optional.of(account));
    return account;
  }
Instantiates a new Simple world.

@param parent the parent
evm/src/main/java/org/hyperledger/besu/evm/fluent/SimpleWorld.java