Fix reload bots

runtime/bin/vmservice/loader.dart

Index: runtime/bin/vmservice/loader.dart
diff --git a/runtime/bin/vmservice/loader.dart b/runtime/bin/vmservice/loader.dart
index 8439b8aad3f6536b891bdeae8a9e330a2cb09e74..8d56466ae6578f7ae152709a20fd25388c8cc92c 100644
--- a/runtime/bin/vmservice/loader.dart
+++ b/runtime/bin/vmservice/loader.dart
@@ -93,6 +93,9 @@ class IsolateLoaderState extends IsolateEmbedderData {
   }
 
   void updatePackageMap(String packagesConfigFlag) {
+    if (packagesConfigFlag == null) {
+      return;
+    }
     _packageMap = null;
     _setPackagesConfig(packagesConfigFlag);
   }