@Override
  public String toString() {
    final StringBuilder sb = new StringBuilder();
    sb.append("ProcessableBlockHeader{");
    sb.append("number=").append(number).append(", ");
    sb.append("parentHash=").append(parentHash).append(", ");
    sb.append("coinbase=").append(coinbase).append(", ");
    sb.append("difficulty=").append(difficulty).append(", ");
    sb.append("gasLimit=").append(gasLimit).append(", ");
    sb.append("timestamp=").append(timestamp).append(", ");
    sb.append("baseFee=").append(baseFee).append(", ");
    sb.append("mixHashOrPrevRandao=").append(mixHashOrPrevRandao).append(", ");
    if (parentBeaconBlockRoot != null) {
      sb.append("parentBeaconBlockRoot=").append(parentBeaconBlockRoot).append(", ");
    }
    return sb.append("}").toString();
  }
Returns the parent beacon block root.

@return the parent beacon block root.
ethereum/core/src/main/java/org/hyperledger/besu/ethereum/core/ProcessableBlockHeader.java