logback-android/src/main/java/ch/qos/logback/core/android/AndroidContextUtil.java
@TargetApi(21)
  public String getNoBackupFilesDirectoryPath() {
    return Build.VERSION.SDK_INT >= 21 &&
            this.context != null
            ? absPath(this.context.getNoBackupFilesDir())
            : "";
  }
@TargetApi(21)
  public String getNoBackupFilesDirectoryPath() {
    return Build.VERSION.SDK_INT >= 21 &&
            this.context != null
            ? absPath(this.context.getNoBackupFilesDir())
            : "";
  }
Returns the absolute path to the directory on the Android
filesystem similar to {@link #getFilesDirectoryPath()}.
The difference is these files are excluded from automatic
backup to remote storage by {@code android.app.backup.BackupAgent}.
This API is only available on SDK 21+. On older versions,
this function returns an empty string.

@return the absolute path to the files directory
(example: "/data/data/com.example/nobackup/files")