code: protected final void copyBitcoinHeaderTo(final Block block) {
          block.nonce = nonce;
          block.prevBlockHash = prevBlockHash;
          block.merkleRoot = getMerkleRoot();
          block.version = version;
          block.time = time;
          block.difficultyTarget = difficultyTarget;
          block.transactions = null;
          block.hash = getHash();
      }
docs: Copy the block without transactions into the provided empty block.