Fixed support library references

app/src/main/java/eu/faircode/email/ActivityBilling.java

@@ -42,6 +42,7 @@ import com.google.android.material.snackbar.Snackbar;
 import java.security.NoSuchAlgorithmException;
 import java.util.List;
 
+import androidx.annotation.Nullable;
 import androidx.localbroadcastmanager.content.LocalBroadcastManager;
 
 abstract class ActivityBilling extends ActivityBase implements PurchasesUpdatedListener {
@@ -192,7 +193,7 @@ abstract class ActivityBilling extends ActivityBase implements PurchasesUpdatedL
     };
 
     @Override
-    public void onPurchasesUpdated(int responseCode, @android.support.annotation.Nullable List<Purchase> purchases) {
+    public void onPurchasesUpdated(int responseCode, @Nullable List<Purchase> purchases) {
         String text = Helper.getBillingResponseText(responseCode);
         Log.i(Helper.TAG, "IAB purchases updated response=" + text);
         if (responseCode == BillingClient.BillingResponse.OK)

app/src/main/java/eu/faircode/email/Helper.java

@@ -33,7 +33,6 @@ import android.net.Uri;
 import android.os.Build;
 import android.os.PowerManager;
 import android.preference.PreferenceManager;
-import android.support.annotation.NonNull;
 import android.text.TextUtils;
 import android.util.Log;
 import android.view.Menu;
@@ -68,6 +67,7 @@ import javax.mail.AuthenticationFailedException;
 import javax.mail.MessagingException;
 import javax.mail.internet.InternetAddress;
 
+import androidx.annotation.NonNull;
 import androidx.appcompat.app.AlertDialog;
 import androidx.browser.customtabs.CustomTabsIntent;
 

gradle.properties

@@ -12,3 +12,6 @@
 # http://www.gradle.org/docs/current/userguide/multi_project_builds.html#sec:decoupled_projects
 # org.gradle.parallel=true
 org.gradle.jvmargs=-Xmx512m
+
+android.useAndroidX=true
+android.enableJetifier=true