@Override
                public void disposeTracer(final OperationTracer tracer) throws IOException {
                  if (outputStreams.containsKey(tracer)) {
                    outputStreams.remove(tracer).close();
                  }
                }
Default constructor for the T8nServerSubCommand class. This constructor is required by PicoCLI
and assigns null to parentCommand.
ethereum/evmtool/src/main/java/org/hyperledger/besu/evmtool/T8nServerSubCommand.java