code: @Override
    public String expand(Map<String, ?> variables) {
      String name = this.name.expand(variables);
      return this.queryString(name, super.expand(variables));
    }
docs: Expand this template. Unresolved variables are removed. If all values remain unresolved, the
  result is an empty string.
  
  @param variables containing the values for expansion.
  @return the expanded template.