getModule API may return null module

Summary:
The native module might be null, and that should not be an exception thrown by the subclassed method.

Changelog:
[Android][Internal] - Mark getModule API to be nullable

Reviewed By: mdvacca, makovkastar

Differential Revision: D37900294

fbshipit-source-id: a4ecc9804b95bf0512554e96985f272b435e33b2

Author: ryancat

ReactAndroid/src/main/java/com/facebook/react/TurboReactPackage.java

@@ -8,6 +8,7 @@
 package com.facebook.react;
 
 import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
 import com.facebook.react.bridge.ModuleHolder;
 import com.facebook.react.bridge.ModuleSpec;
 import com.facebook.react.bridge.NativeModule;
@@ -42,7 +43,8 @@ public List<NativeModule> createNativeModules(ReactApplicationContext reactConte
    * @param reactContext
    * @return
    */
-  public abstract NativeModule getModule(String name, final ReactApplicationContext reactContext);
+  public abstract @Nullable NativeModule getModule(
+      String name, final ReactApplicationContext reactContext);
 
   /**
    * This is a temporary method till we implement TurboModules. Once we implement TurboModules, we