code: public String getRequiredQueryStringParam(final String paramname)
      throws BadRequestException {
      final String value = getQueryStringParam(paramname);
      if (value == null || value.isEmpty()) {
        throw BadRequestException.missingParameter(paramname);
      }
      return value;
    }
docs: Returns the non-empty value of the given required query string parameter.
  <p>
  If this parameter occurs multiple times in the URL, only the last value
  is returned and others are silently ignored.
  @param paramname Name of the query string parameter to get.
  @return The value of the parameter.
  @throws BadRequestException if this query string parameter wasn't passed
  or if its last occurrence had an empty value ({@code &amp;a=}).