code: @Override
      public boolean containsValue(Object runner) {
          if (runner == null) {
              return false;
          }
          Map<String, GroovyRunner> map = getMap();
          readLock.lock();
          try {
              return map.containsValue(runner);
          } finally {
              readLock.unlock();
          }
      }
docs: Returns {@code true} if registry contains the given
  runner instance.
  
  @param runner instance of a GroovyRunner
  @return {@code true} if the given runner is registered