After upgrading Firebase libraries to 

```
implementation "com.google.firebase:firebase-messaging:18.0.0"
implementation 'com.google.firebase:firebase-config:17.0.0'
implementation 'com.google.firebase:firebase-core:16.0.9'

```

and syncing Gradle, I got warning:

```
'setConfigSettings(FirebaseRemoteConfigSettings!): Unit' is deprecated. Deprecated in Java
'setDeveloperModeEnabled(Boolean): FirebaseRemoteConfigSettings.Builder!' is deprecated. Deprecated in Java

```

in these lines:

```
//Setting Developer Mode enabled to fast retrieve the values
firebaseRemoteConfig.setConfigSettings(
    FirebaseRemoteConfigSettings.Builder().setDeveloperModeEnabled(BuildConfig.DEBUG)
        .build())

```