private void validateProcessableBlockHeader() {
    checkState(this.parentHash != null, "Missing parent hash");
    checkState(this.coinbase != null, "Missing coinbase");
    checkState(this.difficulty != null, "Missing block difficulty");
    checkState(this.number > -1L, "Missing block number");
    checkState(this.gasLimit > -1L, "Missing gas limit");
  }
A utility class for building block headers.
ethereum/core/src/main/java/org/hyperledger/besu/ethereum/core/BlockHeaderBuilder.java