public Optional<BlockHeader> getOmmer(final Hash blockHeaderHash, final int index) {
    return blockchain.getBlockBody(blockHeaderHash).map(blockBody -> getOmmer(blockBody, index));
  }
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