Fix v2 licensing

We forced the `extraParams` bundle to be non-null in Kotlin, but it was
indeed null.

Author: fynngodau

vending-app/src/main/java/com/android/vending/licensing/LicensingService.kt

@@ -58,7 +58,7 @@ class LicensingService : Service() {
         override fun checkLicenseV2(
             packageName: String,
             listener: ILicenseV2ResultListener,
-            extraParams: Bundle
+            extraParams: Bundle?
         ): Unit = runBlocking {
             Log.v(TAG, "checkLicenseV2($packageName, $extraParams)")