code: public KSIBuilder setKsiProtocolSignerClient(KSISigningClient signingClient) {
          Util.notNull(signingClient, "KSI Signing Client");
          return setKsiProtocolSigningService(new KSISigningClientServiceAdapter(signingClient));
      }
docs: Sets the signer client to be used in signing process.
  
  @param signingClient
  instance of {@link KSISigningClient}.
  @return Instance of {@link KSIBuilder}.