habitica-self-host/migrations/20141230_new_years_hats.js

db.users.update(
    {'items.gear.owned.head_special_nye':{$ne:null}},
    {$set:{'items.gear.owned.head_special_nye2014':false}},
    {multi:1}
)

db.users.update(
    {'items.gear.owned.head_special_nye':null},
    {$set:{'items.gear.owned.head_special_nye':false}},
    {multi:1}
)