Fix null pointer exception in preference screens

app/src/main/java/org/tasks/files/FileHelper.java

@@ -265,4 +265,14 @@ public class FileHelper {
     }
     return tempName + extension;
   }
+
+  public static String uri2String(@Nullable Uri uri) {
+    if (uri == null) {
+      return "";
+    }
+    if (uri.getScheme().equals(ContentResolver.SCHEME_FILE)) {
+      return new File(uri.getPath()).getAbsolutePath();
+    }
+    return uri.toString();
+  }
 }

app/src/main/java/org/tasks/jobs/BackupWork.java

@@ -6,6 +6,7 @@ import static com.google.common.collect.Lists.newArrayList;
 import static com.todoroo.andlib.utility.DateUtilities.now;
 import static java.util.Collections.emptyList;
 
+import android.content.ContentResolver;
 import android.content.Context;
 import android.net.Uri;
 import androidx.annotation.NonNull;
@@ -102,8 +103,11 @@ public class BackupWork extends RepeatingWorker {
 
   private void deleteOldLocalBackups() {
     Uri uri = preferences.getBackupDirectory();
+    if (uri == null) {
+      return;
+    }
     switch (uri.getScheme()) {
-      case "content":
+      case ContentResolver.SCHEME_CONTENT:
         DocumentFile dir = DocumentFile.fromTreeUri(context, uri);
         for (DocumentFile file : getDeleteList(dir.listFiles())) {
           if (!file.delete()) {
@@ -111,7 +115,7 @@ public class BackupWork extends RepeatingWorker {
           }
         }
         break;
-      case "file":
+      case ContentResolver.SCHEME_FILE:
         File astridDir = new File(uri.getPath());
         File[] fileArray = astridDir.listFiles(FILE_FILTER);
         for (File file : getDeleteList(fileArray, DAYS_TO_KEEP_BACKUP)) {

app/src/main/java/org/tasks/preferences/BasicPreferences.java

@@ -5,6 +5,7 @@ import static com.todoroo.andlib.utility.AndroidUtilities.atLeastLollipop;
 import static org.tasks.dialogs.ExportTasksDialog.newExportTasksDialog;
 import static org.tasks.dialogs.ImportTasksDialog.newImportTasksDialog;
 import static org.tasks.files.FileHelper.newFilePickerIntent;
+import static org.tasks.files.FileHelper.uri2String;
 import static org.tasks.locale.LocalePickerDialog.newLocalePickerDialog;
 import static org.tasks.themes.ThemeColor.LAUNCHERS;
 
@@ -19,7 +20,6 @@ import android.preference.Preference;
 import com.google.common.base.Strings;
 import com.todoroo.astrid.core.OldTaskPreferences;
 import com.todoroo.astrid.reminders.ReminderPreferences;
-import java.io.File;
 import javax.inject.Inject;
 import org.tasks.BuildConfig;
 import org.tasks.R;
@@ -328,14 +328,8 @@ public class BasicPreferences extends InjectingPreferenceActivity
   }
 
   private void updateBackupDirectory() {
-    findPreference(getString(R.string.p_backup_dir)).setSummary(getBackupDirectory());
-  }
-
-  private String getBackupDirectory() {
-    Uri uri = preferences.getBackupDirectory();
-    return uri.getScheme().equals("file")
-        ? new File(uri.getPath()).getAbsolutePath()
-        : uri.toString();
+    findPreference(getString(R.string.p_backup_dir))
+        .setSummary(uri2String(preferences.getBackupDirectory()));
   }
 
   private void setLauncherIcon(int index) {

app/src/main/java/org/tasks/preferences/MiscellaneousPreferences.java

@@ -2,6 +2,7 @@ package org.tasks.preferences;
 
 import static com.todoroo.andlib.utility.AndroidUtilities.atLeastLollipop;
 import static org.tasks.PermissionUtil.verifyPermissions;
+import static org.tasks.files.FileHelper.uri2String;
 
 import android.content.Intent;
 import android.net.Uri;
@@ -10,7 +11,6 @@ import android.preference.CheckBoxPreference;
 import android.speech.tts.TextToSpeech;
 import androidx.annotation.NonNull;
 import com.todoroo.astrid.voice.VoiceOutputAssistant;
-import java.io.File;
 import javax.inject.Inject;
 import org.tasks.R;
 import org.tasks.files.FileHelper;
@@ -99,14 +99,8 @@ public class MiscellaneousPreferences extends InjectingPreferenceActivity {
   }
 
   private void updateAttachmentDirectory() {
-    findPreference(getString(R.string.p_attachment_dir)).setSummary(getAttachmentDirectory());
-  }
-
-  private String getAttachmentDirectory() {
-    Uri uri = preferences.getAttachmentsDirectory();
-    return uri.getScheme().equals("file")
-        ? new File(uri.getPath()).getAbsolutePath()
-        : uri.toString();
+    findPreference(getString(R.string.p_attachment_dir))
+        .setSummary(uri2String(preferences.getAttachmentsDirectory()));
   }
 
   private void initializeCalendarReminderPreference() {

app/src/main/java/org/tasks/preferences/Preferences.java

@@ -6,6 +6,7 @@ import static com.google.common.collect.Sets.newHashSet;
 import static com.todoroo.andlib.utility.AndroidUtilities.atLeastKitKat;
 import static java.util.Collections.emptySet;
 
+import android.content.ContentResolver;
 import android.content.Context;
 import android.content.Intent;
 import android.content.SharedPreferences;
@@ -29,6 +30,7 @@ import java.io.File;
 import java.util.Collection;
 import java.util.concurrent.TimeUnit;
 import javax.inject.Inject;
+import org.jetbrains.annotations.Nullable;
 import org.tasks.BuildConfig;
 import org.tasks.R;
 import org.tasks.data.TaskAttachment;
@@ -369,11 +371,19 @@ public class Preferences {
     }
   }
 
-  public Uri getAttachmentsDirectory() {
-    Uri uri = getUri(R.string.p_attachment_dir);
+  public @Nullable Uri getBackupDirectory() {
+    return getDirectory(R.string.p_backup_dir, "backups");
+  }
+
+  public @Nullable Uri getAttachmentsDirectory() {
+    return getDirectory(R.string.p_attachment_dir, TaskAttachment.FILES_DIRECTORY_DEFAULT);
+  }
+
+  private @Nullable Uri getDirectory(int pref, String name) {
+    Uri uri = getUri(pref);
     if (uri != null) {
       switch (uri.getScheme()) {
-        case "file":
+        case ContentResolver.SCHEME_FILE:
           File file = new File(uri.getPath());
           try {
             if (file.canWrite()) {
@@ -382,7 +392,7 @@ public class Preferences {
           } catch (SecurityException ignored) {
           }
           break;
-        case "content":
+        case ContentResolver.SCHEME_CONTENT:
           if (hasWritePermission(context, uri)) {
             return uri;
           }
@@ -391,15 +401,21 @@ public class Preferences {
     }
 
     if (atLeastKitKat()) {
-      return DocumentFile.fromFile(context.getExternalFilesDir(null))
-          .createDirectory(TaskAttachment.FILES_DIRECTORY_DEFAULT)
-          .getUri();
-    } else {
-      return Uri.fromFile(getDefaultFileLocation(TaskAttachment.FILES_DIRECTORY_DEFAULT));
+      DocumentFile file =
+          DocumentFile.fromFile(context.getExternalFilesDir(null)).createDirectory(name);
+      if (file != null) {
+        return file.getUri();
+      }
+    }
+
+    File file = getDefaultFileLocation(name);
+    if (file != null) {
+      return Uri.fromFile(file);
     }
+    return null;
   }
 
-  private File getDefaultFileLocation(String type) {
+  private @Nullable File getDefaultFileLocation(String type) {
     File externalFilesDir = context.getExternalFilesDir(null);
     if (externalFilesDir == null) {
       return null;
@@ -417,36 +433,6 @@ public class Preferences {
     }
   }
 
-  public Uri getBackupDirectory() {
-    Uri uri = getUri(R.string.p_backup_dir);
-    if (uri != null) {
-      switch (uri.getScheme()) {
-        case "file":
-          File file = new File(uri.getPath());
-          try {
-            if (file.canWrite()) {
-              return uri;
-            }
-          } catch (SecurityException ignored) {
-          }
-          break;
-        case "content":
-          if (hasWritePermission(context, uri)) {
-            return uri;
-          }
-          break;
-      }
-    }
-
-    if (atLeastKitKat()) {
-      return DocumentFile.fromFile(context.getExternalFilesDir(null))
-          .createDirectory("backups")
-          .getUri();
-    } else {
-      return Uri.fromFile(getDefaultFileLocation("backups"));
-    }
-  }
-
   private boolean hasWritePermission(Context context, Uri uri) {
     return PackageManager.PERMISSION_GRANTED
         == context.checkUriPermission(