feat(bigtable): add "TypeUnspecified" to represent an unspecified type (#10820)

Author: steveniemitz

bigtable/type.go

@@ -56,6 +56,13 @@ func Equal(a, b Type) bool {
 	return proto.Equal(a.proto(), b.proto())
 }
 
+// TypeUnspecified represents the absence of a type.
+type TypeUnspecified struct{}
+
+func (n TypeUnspecified) proto() *btapb.Type {
+	return &btapb.Type{}
+}
+
 type unknown[T interface{}] struct {
 	wrapped *T
 }
@@ -240,7 +247,9 @@ func ProtoToType(pb *btapb.Type) Type {
 	if pb == nil {
 		return unknown[btapb.Type]{wrapped: nil}
 	}
-
+	if pb.Kind == nil {
+		return TypeUnspecified{}
+	}
 	switch t := pb.Kind.(type) {
 	case *btapb.Type_Int64Type:
 		return int64ProtoToType(t.Int64Type)

bigtable/type_test.go

@@ -184,7 +184,7 @@ func TestNilChecks(t *testing.T) {
 	if val, ok := ProtoToType(nil).(unknown[btapb.Type]); !ok {
 		t.Errorf("got: %T, wanted unknown[btapb.Type]", val)
 	}
-	if val, ok := ProtoToType(&btapb.Type{}).(unknown[btapb.Type]); !ok {
+	if val, ok := ProtoToType(&btapb.Type{}).(TypeUnspecified); !ok {
 		t.Errorf("got: %T, wanted unknown[btapb.Type]", val)
 	}
 
@@ -221,3 +221,13 @@ func TestNilChecks(t *testing.T) {
 		t.Errorf("got: %T, wanted unknown[btapb.Type]", val)
 	}
 }
+
+func TestTypeUnspecified(t *testing.T) {
+	pb := &btapb.Type{}
+	tpe := ProtoToType(pb)
+	assertType(t, tpe, &btapb.Type{})
+	expect := TypeUnspecified{}
+	if tpe != expect {
+		t.Errorf("got: %v, wanted: %v", tpe, expect)
+	}
+}