code: public static CmsShell getTopShell() {
  
          ArrayList<CmsShell> shells = SHELL_STACK.get();
          if (shells.isEmpty()) {
              return null;
          }
          return shells.get(shells.size() - 1);
  
      }
docs: Gets the top of thread-local shell stack, or null if it is empty.
  
  @return the top of the shell stack