MongoDB null field or true/false
===

On MongoDB, when we have fields such as "draft" (yes/no), "published" (yes/no), etc which is the best strategy? Create the field in all the records and put "yes"/"no" values or put the field just where exists? 

    posts: [{_id:1, text:"hello", draft:true},{_id:2 text:"world", draft:false}]

or

    posts: [{_id:1, text:"hello", draft:true},{_id:2 text:"world"}]

Which is faster? It's for a large amount of data.

Best regards, João