List<Bitmap> getAttachments() {
        JSONArray attachments = options.optJSONArray("attachments");
        if (attachments == null) return null;

        List<Bitmap> bitmaps = new ArrayList<Bitmap>();

        for (int index = 0; index < attachments.length(); index++) {
            Bitmap assetBitmap = assetUtil.getBitmap(attachments.optString(index));

            if (assetBitmap == null) continue;

            // Only use the first attachment
            bitmaps.add(assetBitmap);
            break;
        }

        return bitmaps;
    }
Image attachments for image style notifications. Only returns the first item,
as Android does not support multiple attachments like iOS.
@return null if there are no attachments.
src/android/Options.java