@Nullable
  private File findOutputDir(Location location, @Nullable Iterable<URI> sources) {
    File dir = null;
    if (sources != null && location == StandardLocation.CLASS_OUTPUT) {
      for (URI uri : sources) {
        dir = getSingleOutputDirectory(location, uri);
        if (dir != null) {
          break;
        }
      }
    }
    if (dir == null) {
      dir = getSingleOutputDirectory(location, null);
    }
    return dir;
  }
@Nullable
  private File findOutputDir(Location location, @Nullable Iterable<URI> sources)