@NonNull
    static String getImageUrl(List<FastDocumentFile> files, Uri folderUri) {
        // look for special file names
        for (String iconLocation : PREFERRED_FEED_IMAGE_FILENAMES) {
            for (FastDocumentFile file : files) {
                if (iconLocation.equals(file.getName())) {
                    return file.getUri().toString();
                }
            }
        }

        // use the first image in the folder if existing
        for (FastDocumentFile file : files) {
            String mime = file.getType();
            if (mime != null && (mime.startsWith("image/jpeg") || mime.startsWith("image/png"))) {
                return file.getUri().toString();
            }
        }

        // use default icon as fallback
        return Feed.PREFIX_GENERATIVE_COVER + folderUri;
    }
@Test
    public void testGetImageUrl_NoImageButAudioFiles() {
        List<FastDocumentFile> folder = Collections.singletonList(mockDocumentFile("audio.mp3", "audio/mp3"));
        String imageUrl = LocalFeedUpdater.getImageUrl(folder, Uri.EMPTY);
        assertThat(imageUrl, startsWith(Feed.PREFIX_GENERATIVE_COVER));
    }