db.users.update(
  {'items.pets.Turkey-Base':{$ne:null}},
  {$set:{'items.mounts.Turkey-Base':true}},
  {multi:1}
)

db.users.update(
  {'items.pets.Turkey-Base':null},
  {$set:{'items.pets.Turkey-Base':5}},
  {multi:1}
)