code: @Override
      public GroovyRunner remove(Object key) {
          if (key == null) {
              return null;
          }
          Map<String, GroovyRunner> map = getMap();
          writeLock.lock();
          try {
              cachedValues = null;
              return map.remove(key);
          } finally {
              writeLock.unlock();
          }
      }
docs: Removes a registered runner from the registry.
  
  @param key of the runner to remove
  @return the runner instance that was removed, if no runner
  instance was removed then {@code null}