Make FakeServiceUser assoc methods tolerant of nil

app/models/service_user.rb

@@ -44,7 +44,11 @@ class FakeServiceUser < HashWithIndifferentAccess
 
   ServiceUser.reflect_on_all_associations.each do |assoc|
     define_method assoc.name do
-      assoc.klass.find(self[assoc.primary_key_name])
+      if associated_id = self[assoc.primary_key_name]
+        assoc.klass.find(associated_id)
+      else
+        nil
+      end
     end
   end
 end

spec/models/service_user_spec.rb

@@ -137,5 +137,10 @@ describe FakeServiceUser do
       Person.should_receive(:find).with(@data[5]).and_return person
       @fake.person.should == person
     end
+
+    it 'does not error on an association with no id' do
+      @fake[:person_id] = nil
+      lambda{ @fake.person }.should_not raise_error
+    end
   end
 end