Push notifications: NPE if google-services.json is not found

[jperedadnr]

google-services.json is needed for Android, but if it is not present it causes a NPE:

10-29 12:31:11.799  7338 11290 D GraalCompiled: WARNING: Failed to read google-services.json. Make sure to add the file to the folder: src/android/resources
10-29 12:31:11.799  7338 11290 D GraalCompiled: java.lang.NullPointerException
10-29 12:31:11.799  7338 11290 D GraalCompiled: 	at org.glassfish.json.UnicodeDetectingInputStream.fillBuf(UnicodeDetectingInputStream.java:65)
10-29 12:31:11.799  7338 11290 D GraalCompiled: 	at org.glassfish.json.UnicodeDetectingInputStream.detectEncoding(UnicodeDetectingInputStream.java:104)
10-29 12:31:11.799  7338 11290 D GraalCompiled: 	at org.glassfish.json.UnicodeDetectingInputStream.<init>(UnicodeDetectingInputStream.java:51)
10-29 12:31:11.799  7338 11290 D GraalCompiled: 	at org.glassfish.json.JsonParserImpl.<init>(JsonParserImpl.java:71)
10-29 12:31:11.799  7338 11290 D GraalCompiled: 	at org.glassfish.json.JsonReaderImpl.<init>(JsonReaderImpl.java:49)
10-29 12:31:11.799  7338 11290 D GraalCompiled: 	at org.glassfish.json.JsonProviderImpl.createReader(JsonProviderImpl.java:112)
10-29 12:31:11.799  7338 11290 D GraalCompiled: 	at javax.json.Json.createReader(Json.java:201)
10-29 12:31:11.799  7338 11290 D GraalCompiled: 	at com.gluonhq.attach.pushnotifications.impl.AndroidPushNotificationsService.readGoogleServicesConfiguration(AndroidPushNotificationsService.java:97)
10-29 12:31:11.799  7338 11290 D GraalCompiled: 	at com.gluonhq.attach.pushnotifications.impl.AndroidPushNotificationsService.register(AndroidPushNotificationsService.java:84)

This should be avoided.

[tiainen]

This exception is already correctly handled. The actual fatal crash happens later on when trying to initialize Firebase in DalvikPushNotificationsService.initializeFirebase():

10-29 12:31:11.799  7338 11292 F com.d: java_vm_ext.cc:577] JNI DETECTED ERROR IN APPLICATION: JNI NewStringUTF called with pending exception java.lang.IllegalArgumentException: ApplicationId must be set.
10-29 12:31:11.799  7338 11292 F com.d: java_vm_ext.cc:577]   at java.lang.String com.google.android.gms.common.internal.Preconditions.checkNotEmpty(java.lang.String, java.lang.Object) ((null):8)
10-29 12:31:11.799  7338 11292 F com.d: java_vm_ext.cc:577]   at com.google.firebase.FirebaseOptions$Builder com.google.firebase.FirebaseOptions$Builder.setApplicationId(java.lang.String) (com.google.firebase:firebase-common@@19.3.0:87)
10-29 12:31:11.799  7338 11292 F com.d: java_vm_ext.cc:577]   at void com.gluonhq.helloandroid.DalvikPushNotificationsService.initializeFirebase(java.lang.String, java.lang.String, java.lang.String, java.lang.String) (DalvikPushNotificationsService.java:93)

[jperedadnr]

Right, in any case:
we should prevent the NPE (by checking that the file exists before calling Json.createReader(), and also prevent the JNI error by not passing an empty configuration to Firebase.