@Override
    public RewardTrace build() {
      return new RewardTrace(
          getActionBuilder(),
          getResultBuilder(),
          getSubtraces(),
          getTraceAddress(),
          getType(),
          getBlockNumber(),
          getBlockHash(),
          getTransactionPosition(),
          getTransactionHash(),
          getError());
    }
We have to override the {@link FlatTrace} method because in the case of a reward the
transactionPosition value must be returned even if it is null

@return transactionPosition
ethereum/api/src/main/java/org/hyperledger/besu/ethereum/api/jsonrpc/internal/results/tracing/flat/RewardTrace.java