Conversion goal "Time On Page" can cause intermittent exception

Description

Steps to reproduce:
1. Edit a page and create an A/B test.
2. Use "Time on page" conversion goal with settings 60 seconds, 50% participation percentage, and 30 days for instance.
3. Start the test.
4. Visit the page a couple of times if you can't see it the first time.

Expected:
Should show different versions of the page.

Actual:
Get exception when visiting one of the versions (either A or B):

[NullReferenceException: Object reference not set to an instance of an object.]
   EPiServer.Marketing.Testing.Web.ClientKPI.ClientKpiInjector.AppendClientKpiScript() +605
   EPiServer.Marketing.Testing.Web.TestHandlerInitializer.onPostReleaseRequestState(Object sender, EventArgs e) +11
   System.Web.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +141
   System.Web.HttpApplication.ExecuteStepImpl(IExecutionStep step) +48
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +71