diff --git a/src/spawn.ts b/src/spawn.ts
index 9ae72adb..33c3b41b 100644
--- a/src/spawn.ts
+++ b/src/spawn.ts
@@ -9,7 +9,7 @@ export class Spawner {
 
   output = ""
   buffer = ""
-  exitCode: number | null = null
+  exitCode: number | undefined = undefined
 
   onData = (data: string) => {
     data