code: function reformatUpdateProperty(next) {
      const document = this._update['$set'];
  
      if (document) {
        paths.forEach(function(path) {
          try {
            const splitted = path.path.split('.');
            const key      = splitted.shift();
  
            if (document[key] === undefined) { return; }
  
            const value   = determineValue(splitted, document[key]);
  
            document[key] = nest(splitted, value);
          } catch (error) { return next(error); }
        });
      }
  
      next();
    }
docs: If a document is modified, this method will locate the value on updates and assign it to the
  appropriate property, allowing for proper validations later.
  @param <Function>: next - function that notifies mongoose this middleware is complete