Rails form select with NULL (no choice) support -

How do I add a tap option to select my form? I have a table:

  categories id category_id name   
 If I am creating a new category, then I  NO_CATEGORY  Option (zero value and id).  
 My view code:  
  & lt;% = f.collection_select: supercategory_id, category all,: id,: name% & gt;   
 Besides, is this a good idea? Is not it better for some predefined root category in the database? Thank you.   
 
 
 Try:  
    
 It's okay to be zero. Just know its model logic that it should create a new category and choose it instead of assigning it to the mass rather than assign it. There may be something that happens in the pre_translation method