protosanitizer: only overwrite secret fields if already set

The previous version was adding "secrets: *** strippped ***"
even when the "secrets" field was unset.

Author: pohly

protosanitizer/protosanitizer.go

@@ -95,7 +95,10 @@ func strip(parsed interface{}, msg interface{}) {
 		for _, field := range fields {
 			ex, err := proto.GetExtension(field.Options, csi.E_CsiSecret)
 			if err == nil && ex != nil && *ex.(*bool) {
-				parsedFields[field.GetName()] = "***stripped***"
+				// Overwrite only if already set.
+				if _, ok := parsedFields[field.GetName()]; ok {
+					parsedFields[field.GetName()] = "***stripped***"
+				}
 			} else if field.GetType() == protobuf.FieldDescriptorProto_TYPE_MESSAGE {
 				// When we get here,
 				// the type name is something like ".csi.v1.CapacityRange" (leading dot!)

protosanitizer/protosanitizer_test.go

@@ -70,6 +70,7 @@ func TestStripSecrets(t *testing.T) {
 		{"hello world", `"hello world"`},
 		{true, "true"},
 		{false, "false"},
+		{&csi.CreateVolumeRequest{}, `{}`},
 		// Test case from https://github.com/kubernetes-csi/csi-lib-utils/pull/1#pullrequestreview-180126394.
 		{&csi.CreateVolumeRequest{
 			Name: "test-volume",