how to add link to null path in menu in drupal 7
You can use the Special menu items module. 


  Features:
  
  
  User can create a new menu item and place either "&#60;nolink>" or "&#60;separator>" to the Path field, without quotes.
  "&#60;nolink>" item will be rendered similar to a normal menu link item but there will be no link just the title.
  You can change HTML tag used for menu item
  "&#60;separator>" item will be rendered to an item which is no link and by default title will be "-------".
  Breadcrumb of "&#60;nolink>" will be rendered same as "&#60;nolink>" menu item.
  CSS class "nolink" is added to "nolink" menu item.
  CSS class "separator" is added to "separator" menu item.