Update snapshot parent filter property to always exist

The parent property may be empty but always exists.

Signed-off-by: Derek McGowan <derek@mcgstyle.net>

metadata/adaptors.go

@@ -159,9 +159,7 @@ func adaptSnapshot(info snapshots.Info) filters.Adaptor {
 		case "name":
 			return info.Name, true
 		case "parent":
-			if info.Parent != "" {
-				return info.Parent, true
-			}
+			return info.Parent, true
 		case "labels":
 			return checkMap(fieldpath[1:], info.Labels)
 		}

snapshots/storage/bolt.go

@@ -633,9 +633,7 @@ func adaptSnapshot(info snapshots.Info) filters.Adaptor {
 		case "name":
 			return info.Name, true
 		case "parent":
-			if info.Parent != "" {
-				return info.Parent, true
-			}
+			return info.Parent, true
 		case "labels":
 			if len(info.Labels) == 0 {
 				return "", false

snapshots/testsuite/testsuite.go

@@ -1061,7 +1061,7 @@ func checkWalk(ctx context.Context, t *testing.T, snapshotter snapshots.Snapshot
 		},
 		{
 			matches: []string{"a", "v", "a-wl", "v-wl"},
-			filters: []string{"parent,labels.\"containerd.io/gc.root\"==check-walk"},
+			filters: []string{"parent!=\"\",labels.\"containerd.io/gc.root\"==check-walk"},
 		},
 		{
 			matches: []string{"p-wl", "a-wl", "v-wl", "a-np-wl"},