Fix recent reload flakes

runtime/vm/service.cc

Index: runtime/vm/service.cc
diff --git a/runtime/vm/service.cc b/runtime/vm/service.cc
index 05f7fcdeba7ed62dbe0af5b77cf20021f312a966..eeb6d23c661a1e4db9eaa0e543704fbecc5d1fca 100644
--- a/runtime/vm/service.cc
+++ b/runtime/vm/service.cc
@@ -2543,9 +2543,11 @@ RawError* Service::MaybePause(Isolate* isolate, const Error& error) {
   if (!isolate->IsPaused()) {
     if (isolate->should_pause_post_service_request()) {
       isolate->set_should_pause_post_service_request(false);
-      // Before pausing, restore the sticky error. The debugger will return it
-      // from PausePostRequest.
-      Thread::Current()->set_sticky_error(error);
+      if (!error.IsNull()) {
+        // Before pausing, restore the sticky error. The debugger will return it
+        // from PausePostRequest.
+        Thread::Current()->set_sticky_error(error);
+      }
       return isolate->PausePostRequest();
     }
   }