code: public ArgumentListBuilder add(String a, boolean mask) {
          if(a!=null) {
              if(mask) {
                  this.mask.set(args.size());
              }
              args.add(a);
          }
          return this;
      }
docs: Optionally hide this part of the command line from being printed to the log.
  @param a a command argument
  @param mask true to suppress in output, false to print normally
  @return this
  @see hudson.Launcher.ProcStarter#masks(boolean[])
  @see Launcher#maskedPrintCommandLine(List, boolean[], FilePath)
  @since 1.378