private BlockHeader getOmmer(final BlockBody blockBody, final int index) {
    final List<BlockHeader> ommers = blockBody.getOmmers();
    if (ommers.size() > index) {
      return ommers.get(index);
    } else {
      return null;
    }
  }
Returns the ommer at the given index for the referenced block.

@param blockHeaderHash The hash of the block to be queried.
@param index The index of the ommer in the blocks ommers list.
@return The ommer at the given index belonging to the referenced block.
ethereum/api/src/main/java/org/hyperledger/besu/ethereum/api/query/BlockchainQueries.java