IT Shop overview search returns an error: "Object reference not set to an instance of an object" (4320933)

After searching from the top navigation header within IT Shop, and navigating to a product in the search result (product overview), clicking the "Results for:" navigation link results in the following error:

"There was an error processing your request. Please contact your system administrator."

In the log:

UnhandledException Object reference not set to an instance of an object.

At VI.WebDesigner.Runtime.Consequences.RenderPartialPageConsequence.WriteTo (XmlTextWriter xmlw, IHttpContext httpcontext, IDocumentUpdate documentUpdate)

At VI.WebDesigner.Runtime.UpdateDocumentGenerator.WriteTo (Stream str, Encoding enc, IHttpContext httpContext, IEnumerable`1 checkpoints, Boolean closeStream)