Warn when Audited.current_user_method references undefined method

lib/audited/sweeper.rb

@@ -20,7 +20,16 @@ def around(controller)
     end
 
     def current_user
-      lambda { controller.send(Audited.current_user_method) if controller.respond_to?(Audited.current_user_method, true) }
+      lambda {
+        method = Audited.current_user_method
+        if controller.respond_to?(method, true)
+          controller.send(method)
+        else
+          warn "[audited] #{controller.class}##{method} is not defined. " \
+              "Audit records will have a nil user."
+          nil
+        end
+      }
     end
 
     def remote_ip

spec/audited/sweeper_spec.rb

@@ -47,12 +47,14 @@ def populate_user
       expect(controller.company.audits.last.user).to eq(user)
     end
 
-    it "does not audit when method is not found" do
+    it "warns and sets nil user when method is not found" do
       controller.send(:current_user=, user)
       Audited.current_user_method = :nope
       expect {
-        post :create
-      }.to change(Audited::Audit, :count)
+        expect {
+          post :create
+        }.to change(Audited::Audit, :count)
+      }.to output(/\[audited\].*nope.*not defined/).to_stderr
       expect(controller.company.audits.last.user).to eq(nil)
     end