code: @Override
      public boolean containsKey(Object key) {
          if (key == null) {
              return false;
          }
          Map<String, GroovyRunner> map = getMap();
          readLock.lock();
          try {
              return map.containsKey(key);
          } finally {
              readLock.unlock();
          }
      }
docs: Returns {@code true} if a runner was registered with the
  specified key.
  
  @param key for the registered runner
  @return {@code true} if a runner was registered with given key