diff --git a/src/processTSClientOutput.go b/src/processTSClientOutput.go
index f47c662..263c603 100644
--- a/src/processTSClientOutput.go
+++ b/src/processTSClientOutput.go
@@ -162,7 +162,7 @@ async function InvokeOk(path: string, method: HTMLMethod, body?: any): Promise<b
 			if f.Desc != "" {
 				b.WriteString(fmt.Sprintf("\t/**\n%s*/\n", f.Desc))
 			}
-			b.WriteString(fmt.Sprintf("\t%s:%s\n", strings.ToLower(kf), ftype))
+			b.WriteString(fmt.Sprintf("\t%s ?: %s\n", strings.ToLower(kf), ftype))
 		}
 
 		b.WriteString(fmt.Sprintf("}\n\n"))