protected URL getFileURL(License license, String filename) throws IOException {

    URL licenseBaseURL = license.getBaseURL();
    URL result = MojoHelper.getUrl(licenseBaseURL, filename);
    if (!checkExists(result)) {
      // let's try with a .ftl suffix
      URL resultWithFtlSuffix =
          MojoHelper.getUrl(licenseBaseURL, filename + License.TEMPLATE_SUFFIX);

      if (checkExists(resultWithFtlSuffix)) {
        result = resultWithFtlSuffix;
      } else {
        throw new IllegalArgumentException(
            "Could not find license ("
                + license
                + ") content file at ["
                + result
                + "], nor at ["
                + resultWithFtlSuffix
                + "] for resolver "
                + this);
      }
    }
    return result;
  }