Errors and warnings (see attached screenshot) pop up when I go to Lighting -> Baked Lightmaps. It only happen if 1) I am using an developer build and 2) I have at least one lightmap. Only one lightmap is shown even though there are more.

For searchability here is stacktrace:
Exception: Style.Draw may not be called with GUIContent that is null.
UnityEngine.GUIStyle.Draw (Rect position, UnityEngine.GUIContent content, Int32 controlId, Boolean isHover, Boolean isActive, Boolean on, Boolean hasKeyboardFocus) (at C:/Users/rasmusn/Projects/Unity/Modules/IMGUI/GUIStyle.cs:258)
UnityEngine.GUIStyle.Draw (Rect position, UnityEngine.GUIContent content, Boolean isHover, Boolean isActive, Boolean on, Boolean hasKeyboardFocus) (at C:/Users/rasmusn/Projects/Unity/Modules/IMGUI/GUIStyle.cs:238)
UnityEngine.GUI.DoLabel (Rect position, UnityEngine.GUIContent content, UnityEngine.GUIStyle style) (at C:/Users/rasmusn/Projects/Unity/Modules/IMGUI/GUI.cs:971)
UnityEngine.GUI.Label (Rect position, UnityEngine.GUIContent content, UnityEngine.GUIStyle style) (at C:/Users/rasmusn/Projects/Unity/Modules/IMGUI/GUI.cs:139)
UnityEngine.GUILayout.DoLabel (UnityEngine.GUIContent content, UnityEngine.GUIStyle style, UnityEngine.GUILayoutOption[] options) (at C:/Users/rasmusn/Projects/Unity/Modules/IMGUI/GUILayout.cs:16)
UnityEngine.GUILayout.Label (UnityEngine.GUIContent content, UnityEngine.GUIStyle style, UnityEngine.GUILayoutOption[] options) (at C:/Users/rasmusn/Projects/Unity/Modules/IMGUI/GUILayout.cs:14)
UnityEditor.LightingWindowLightmapPreviewTab.LightmapDebugInfo (Int32 index) (at C:/Users/rasmusn/Projects/Unity/Editor/Mono/SceneModeWindows/LightingWindowLightmapPreviewTab.cs:389)
UnityEditor.LightingWindowLightmapPreviewTab.LightmapListGUI (UnityEngine.LightmapData[] lightmaps, UnityEditor.VisualisationGITexture[] realtimeLightmaps) (at C:/Users/rasmusn/Projects/Unity/Editor/Mono/SceneModeWindows/LightingWindowLightmapPreviewTab.cs:157)
UnityEditor.LightingWindowLightmapPreviewTab.OnGUI (Rect position) (at C:/Users/rasmusn/Projects/Unity/Editor/Mono/SceneModeWindows/LightingWindowLightmapPreviewTab.cs:99)
UnityEditor.LightingWindow.OnGUI () (at C:/Users/rasmusn/Projects/Unity/Editor/Mono/SceneModeWindows/LightingWindow.cs:117)
System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Reflection/MonoMethod.cs:222)
Rethrow as TargetInvocationException: Exception has been thrown by the target of an invocation.
System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Reflection/MonoMethod.cs:232)
System.Reflection.MethodBase.Invoke (System.Object obj, System.Object[] parameters) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Reflection/MethodBase.cs:115)
UnityEditor.HostView.Invoke (System.String methodName, System.Object obj) (at C:/Users/rasmusn/Projects/Unity/Editor/Mono/HostView.cs:323)
UnityEditor.HostView.Invoke (System.String methodName) (at C:/Users/rasmusn/Projects/Unity/Editor/Mono/HostView.cs:317)
UnityEditor.HostView.InvokeOnGUI (Rect onGUIPosition, Rect viewRect) (at C:/Users/rasmusn/Projects/Unity/Editor/Mono/HostView.cs:283)