code: protected ContextualStorage getContextualStorage(boolean createIfNotExist, String clientWindowFlowId)
      {
          //FacesContext facesContext = FacesContext.getCurrentInstance();
          //String clientWindowFlowId = getCurrentClientWindowFlowId(facesContext);
          if (clientWindowFlowId == null)
          {
              throw new ContextNotActiveException("FlowScopedContextImpl: no current active flow");
          }
  
          if (createIfNotExist)
          {
              return getFlowScopeBeanHolder().getContextualStorage(beanManager, clientWindowFlowId);
          }
          else
          {
              return getFlowScopeBeanHolder().getContextualStorageNoCreate(beanManager, clientWindowFlowId);
          }
      }
docs: An implementation has to return the underlying storage which
  contains the items held in the Context.
  @param createIfNotExist whether a ContextualStorage shall get created if it doesn't yet exist.
  @return the underlying storage