Error in LightmappingWindow.cs:343

I'm using the free version of unity, and whenever I add a 3d Text GameObject, I get the following error. This happens when I add the text or click anywhere in the GUI. Any ideas?

 NullReferenceException: Object reference not set to an instance of an object
 UnityEditor.LightmappingWindow.HasNormals (UnityEngine.Renderer renderer) (at C:/BuildAgent/work/b0bcff80449a48aa/Editor/Mono/SceneModeWindows/LightmappingWindow.cs:343)
 UnityEditor.LightmappingWindow.ObjectSettings () (at C:/BuildAgent/work/b0bcff80449a48aa/Editor/Mono/SceneModeWindows/LightmappingWindow.cs:398)
 UnityEditor.LightmappingWindow.OnGUI () (at C:/BuildAgent/work/b0bcff80449a48aa/Editor/Mono/SceneModeWindows/LightmappingWindow.cs:197)
 System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture)