diff --git a/flow/fbjs.js b/flow/fbjs.js
new file mode 100644
index 000000000..45cbe8abc
--- /dev/null
+++ b/flow/fbjs.js
@@ -0,0 +1,16 @@
+/**
+ * Copyright (c) 2013-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+declare module 'fbjs/lib/invariant' {
+  declare function exports<T>(condition: any, message: string, ...args: Array<any>): void;
+}
+
+declare module 'fbjs/lib/nullthrows' {
+  declare function exports<T>(value: ?T): T;
+}
diff --git a/local-cli/server/util/inspectorProxy.js b/local-cli/server/util/inspectorProxy.js
index 1cabb62e5..7d29721a9 100644
--- a/local-cli/server/util/inspectorProxy.js
+++ b/local-cli/server/util/inspectorProxy.js
@@ -197,7 +197,7 @@ class Device {
 
   _handleWrappedEvent(event: WrappedEvent) {
     const payload = nullthrows(event.payload);
-    const socket = this._connections.get(payload.pageId);
+    const socket = this._connections.get(nullthrows(payload.pageId));
     if (!socket) {
       console.error('Invalid pageId from device:', payload.pageId);
       return;
diff --git a/packager/react-packager/src/ModuleGraph/worker/collect-dependencies.js b/packager/react-packager/src/ModuleGraph/worker/collect-dependencies.js
index df82ea23c..37e447259 100644
--- a/packager/react-packager/src/ModuleGraph/worker/collect-dependencies.js
+++ b/packager/react-packager/src/ModuleGraph/worker/collect-dependencies.js
@@ -139,5 +139,5 @@ exports.forOptimization =
     collectDependencies(
       ast,
       new ProdReplacement(names),
-      dependencyMapName && types.identifier(dependencyMapName),
+      dependencyMapName ? types.identifier(dependencyMapName) : undefined,
     );