Add method to IFoo for testing NULL interfaces.

Bug: 32410513
Test: mma, hidl_test
Change-Id: I791c3a95e670a859e5e494ead987d2a93f5047a5
diff --git a/tests/foo/1.0/default/Foo.h b/tests/foo/1.0/default/Foo.h
index e61291d..703c210 100644
--- a/tests/foo/1.0/default/Foo.h
+++ b/tests/foo/1.0/default/Foo.h
@@ -56,6 +56,8 @@
     Return<void> haveAVectorOfGenericInterfaces(
             const hidl_vec<sp<android::hardware::IBinder> > &in,
             haveAVectorOfGenericInterfaces_cb _hidl_cb) override;
+
+    Return<void> echoNullInterface(const sp<IFooCallback> &cb, echoNullInterface_cb _hidl_cb) override;
 private:
     std::vector<::native_handle_t *> mHandles;
 };