Collab History Window fails to display, ArgumentNullException error

The full error is quoted below. I’ve tried uninstalling the “Version Control” package and reinstalling. I’ve also tried updating it. I’m using Unity 2019.4.29f1. I used Collab in 2018.4.20f1 and the history window worked fine.

Please help :slight_smile:

ArgumentNullException: Value cannot be null.
Parameter name: styleSheet
UnityEngine.UIElements.VisualElementStyleSheetSet.Add (UnityEngine.UIElements.StyleSheet styleSheet) (at <aea3cceceb0c44ea9855b62119e9be3b>:0)
UnityEditor.CollabHistoryWindow.AddStyleSheetPath (UnityEngine.UIElements.VisualElement root, System.String path) (at Library/PackageCache/com.unity.collab-proxy@1.6.0/Editor/Collaborate/Collab/CollabHistoryWindow.cs:96)
UnityEditor.CollabHistoryWindow.SetupGUI () (at Library/PackageCache/com.unity.collab-proxy@1.6.0/Editor/Collaborate/Collab/CollabHistoryWindow.cs:110)
UnityEditor.CollabHistoryWindow.OnEnable () (at Library/PackageCache/com.unity.collab-proxy@1.6.0/Editor/Collaborate/Collab/CollabHistoryWindow.cs:62)

Ok, here’s what I did:

Load your old 2018.4.20f1. Make a backup of the “Packages” folder.
Then, load 2019.4.29f1. Replace the “Packages” folder in the 2019 version with the “Packages” folder of the 2018 version.
If publishing doesn’t work: Save, close and reopen Unity. (If it still doesn’t work, delete the “temp” folder if it lets you).

Not sure if this will work for you but it did for me. Hope this helps.