Go: fix handling empty tags-set for loading saved model

tensorflow/go/saved_model.go

@@ -17,6 +17,7 @@ limitations under the License.
 package tensorflow
 
 import (
+	"fmt"
 	"runtime"
 	"unsafe"
 
@@ -57,6 +58,9 @@ func LoadSavedModel(exportDir string, tags []string, options *SessionOptions) (*
 		return nil, err
 	}
 	cExportDir := C.CString(exportDir)
+	if len(tags) == 0 {
+		return nil, fmt.Errorf("empty tags are not allowed")
+	}
 	cTags := make([]*C.char, len(tags))
 	for i := range tags {
 		cTags[i] = C.CString(tags[i])

tensorflow/go/saved_model_test.go

@@ -19,7 +19,8 @@ package tensorflow
 import "testing"
 
 func TestSavedModel(t *testing.T) {
-	bundle, err := LoadSavedModel("../cc/saved_model/testdata/half_plus_two/00000123", []string{"serve"}, nil)
+	tags := []string{"serve"}
+	bundle, err := LoadSavedModel("../cc/saved_model/testdata/half_plus_two/00000123", tags, nil)
 	if err != nil {
 		t.Fatalf("LoadSavedModel(): %v", err)
 	}
@@ -30,3 +31,11 @@ func TestSavedModel(t *testing.T) {
 	// TODO(jhseu): half_plus_two has a tf.Example proto dependency to run. Add a
 	// more thorough test when the generated protobufs are available.
 }
+
+func TestSavedModelWithEmptyTags(t *testing.T) {
+	tags := []string{}
+	_, err := LoadSavedModel("../cc/saved_model/testdata/half_plus_two/00000123", tags, nil)
+	if err == nil {
+		t.Fatalf("LoadSavedModel() should return an error if tags are empty")
+	}
+}