docs: public boolean[] toMaskArray() {
          boolean[] mask = new boolean[args.size()];
          for( int i=0; i<mask.length; i++)
              mask[i] = this.mask.get(i);
          return mask;
      }
  
      /**
       * Add a masked argument
       * @param string the argument
       */
      public void addMasked(String string) {
          add(string, true);
      }
  
      public ArgumentListBuilder addMasked(Secret s) {
          return add(Secret.toString(s),true);
      }
  
      /**
       * Debug/error message friendly output.
       */
      public String toString() {
          StringBuilder buf = new StringBuilder();
          for (int i=0; i<args.size(); i++) {
              String arg = args.get(i);
              if (mask.get(i))
                  arg = "******";
  
              if(buf.length()>0)  buf.append(' ');
  
              if(arg.indexOf(' ')>=0 || arg.length()==0)
                  buf.append('"').append(arg).append('"');
              else
                  buf.append(arg);
          }
          return buf.toString();
      }
  
      private static final long serialVersionUID = 1L;
  }