docs: public Closure contents(final Closure cl) {
          return new Closure(cl.getOwner(), cl.getThisObject()) {
              private static final long serialVersionUID = -5733727697043906478L;
  
              @Override
              public Object call() {
                  cl.call();
                  return "";
              }
  
              @Override
              public Object call(final Object... args) {
                  cl.call(args);
                  return "";
              }
  
              @Override
              public Object call(final Object arguments) {
                  cl.call(arguments);
                  return "";
              }
          };
      }