fix potential NPEs

Signed-off-by: tobiaskaminsky <tobias@kaminsky.me>

src/main/java/com/owncloud/android/ui/activity/ContactsPreferenceActivity.java

@@ -37,8 +37,8 @@ import com.evernote.android.job.util.support.PersistableBundleCompat;
 import com.owncloud.android.MainApp;
 import com.owncloud.android.R;
 import com.owncloud.android.datamodel.OCFile;
-import com.owncloud.android.lib.common.utils.Log_OC;
 import com.owncloud.android.jobs.ContactsBackupJob;
+import com.owncloud.android.lib.common.utils.Log_OC;
 import com.owncloud.android.ui.fragment.FileFragment;
 import com.owncloud.android.ui.fragment.contactsbackup.ContactListFragment;
 import com.owncloud.android.ui.fragment.contactsbackup.ContactsBackupFragment;
@@ -76,8 +76,14 @@ public class ContactsPreferenceActivity extends FileActivity implements FileFrag
         boolean showSidebar = getIntent().getBooleanExtra(EXTRA_SHOW_SIDEBAR, true);
         if (!showSidebar) {
             setDrawerLockMode(DrawerLayout.LOCK_MODE_LOCKED_CLOSED);
-            getSupportActionBar().setDisplayHomeAsUpEnabled(true);
-            mDrawerToggle.setDrawerIndicatorEnabled(false);
+
+            if (getSupportActionBar() != null) {
+                getSupportActionBar().setDisplayHomeAsUpEnabled(true);
+            }
+            
+            if (mDrawerToggle != null) {
+                mDrawerToggle.setDrawerIndicatorEnabled(false);
+            }
         }
 
         Intent intent = getIntent();
@@ -100,7 +106,7 @@ public class ContactsPreferenceActivity extends FileActivity implements FileFrag
             transaction.commit();
         }
 
-        BottomNavigationView bottomNavigationView = (BottomNavigationView) findViewById(R.id.bottom_navigation_view);
+        BottomNavigationView bottomNavigationView = findViewById(R.id.bottom_navigation_view);
 
         if (getResources().getBoolean(R.bool.bottom_toolbar_enabled)) {
             bottomNavigationView.setVisibility(View.VISIBLE);