.

wcfs/δbtail.go

@@ -892,13 +892,15 @@ func diffT(ctx context.Context, a, b *Tree, δZTC SetOid, trackIdx map[zodb.Oid]
 				continue // key not covered
 			}
 
-			// XXX check for bnode.node.(*Tree)   (ø tree case)
-
 			// +bucket if that bucket is reached for the first time
 			if !bnode.done {
-				δB, err := diffB(ctx, nil, bnode.node.(*Bucket))
-				if err != nil {
-					return nil, err
+				var δB map[Key]ΔValue
+				bbucket, ok := bnode.node.(*Bucket)
+				if ok { // !ok means ø tree
+					δB, err = diffB(ctx, nil, bbucket)
+					if err != nil {
+						return nil, err
+					}
 				}
 
 				// δ <- δB