code: def release(self, *args, **kwargs):
          
          if not self.field.lockable:
              return
          if self.sub_lock_mode:
              return
          super(FieldLock, self).release(*args, **kwargs)
          self.already_locked_by_model = self.sub_lock_mode = False
docs: Really release the lock only if it's not a sub-lock. Then save the
          sub-lock status and mark the model as unlocked.