Fix recent reload flakes

runtime/vm/service.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/service.h"
 
 #include "include/dart_api.h"
 #include "include/dart_native_api.h"
 #include "platform/globals.h"
 
@@ skipping 2525 matching lines @@
   isolate->set_should_pause_post_service_request(
       BoolParameter::Parse(stream->LookupParam("pause"), false));
 }
 
 
 RawError* Service::MaybePause(Isolate* isolate, const Error& error) {
   // Don't pause twice.
   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();
     }
   }
   return error.raw();
 }
 
 
 static bool AddBreakpointCommon(Thread* thread,
                                 JSONStream* js,
                                 const String& script_uri) {
@@ skipping 1607 matching lines @@
     if (strcmp(method_name, method.name) == 0) {
       return &method;
     }
   }
   return NULL;
 }
 
 #endif  // !PRODUCT
 
 }  // namespace dart