message.rb in mongoid-rspec-4.1.0

- old
+ new

@@ -3,9 +3,15 @@
 
   field :identifier
   field :from
   field :to
 
+  if Mongoid::Compatibility::Version.mongoid6_or_newer?
+    belongs_to :user, optional: true
+  else
+    belongs_to :user
+  end
+
   validates :identifier, uniqueness: { message: 'uniqueness' }
   validates :from, presence: { message: 'required' }
   validates :to, format: { with: /[a-z]+/, message: 'format' }
 end