Error occurs (reproducible) when accepting the reformed caravan inventory selection, to send the caravan to the next point of its travel.

Visual Exception error report:
Exception in Verse.Window.InnerWindowOnGUI: System.NullReferenceException: Object reference not set to an instance of an object
at QualityColors.QualityColorsMod.TryGetQuality (Verse.Thing t, RimWorld.QualityCategory& cat) [0x00001] in <b1b5519dcce14c4b95fe3e6b788643e7>:0
at QualityColors.QualityColorsMod.AddColors (RimWorld.Transferable trad, UnityEngine.Rect idRect, UnityEngine.Color& labelColor) [0x00021] in <b1b5519dcce14c4b95fe3e6b788643e7>:0
at RimWorld.TransferableUIUtility.DrawTransferableInfo (RimWorld.Transferable trad, UnityEngine.Rect idRect, UnityEngine.Color labelColor) [0x0001f] in <b64badbf3c3d41018b3ca5d3e8c77771>:0
- prefix legodude17.QualityColors: Void QualityColors.QualityColorsMod:AddColors(Transferable trad, Rect idRect, Color& labelColor)
at RimWorld.TransferableOneWayWidget.DoRow (UnityEngine.Rect rect, RimWorld.TransferableOneWay trad, System.Int32 index, System.Single availableMass) [0x00511] in <b64badbf3c3d41018b3ca5d3e8c77771>:0
- postfix TimmyLiang.TradeHelper: Void TradeHelper.Main+CaravanPatch3:Postfix(Rect rect, TransferableOneWay trad, Int32 index, Single availableMass)
at RimWorld.TransferableOneWayWidget.FillMainRect (UnityEngine.Rect mainRect, System.Boolean& anythingChanged) [0x0018d] in <b64badbf3c3d41018b3ca5d3e8c77771>:0
at RimWorld.TransferableOneWayWidget.OnGUI (UnityEngine.Rect inRect, System.Boolean& anythingChanged) [0x00196] in <b64badbf3c3d41018b3ca5d3e8c77771>:0
at RimWorld.Dialog_FormCaravan.DoWindowContents (UnityEngine.Rect inRect) [0x002c1] in <b64badbf3c3d41018b3ca5d3e8c77771>:0
- prefix TimmyLiang.TradeHelper: Boolean TradeHelper.Main+CaravanPatch:Prefix(Dialog_FormCaravan __instance, Rect& inRect)
- postfix TimmyLiang.TradeHelper: Void TradeHelper.Main+CaravanPatch:Postfix(Dialog_FormCaravan __instance, Rect& inRect, List`1& ___transferables)
at Verse.Window.InnerWindowOnGUI (System.Int32 x) [0x001f8] in <b64badbf3c3d41018b3ca5d3e8c77771>:0
- transpiler net.pardeike.rimworld.lib.harmony: IEnumerable`1 VisualExceptions.ExceptionsAndActivatorHandler:Transpiler(IEnumerable`1 instructions, MethodBase original)