an class='id identifier rubyid_to_sym'>to_sym</span>
      <span class='kw'>if</span> <span class='op'>!</span><span class='id identifier rubyid_query_string_params'>query_string_params</span><span class='period'>.</span><span class='id identifier rubyid_key?'>key?</span><span class='lparen'>(</span><span class='id identifier rubyid_param_name'>param_name</span><span class='rparen'>)</span>
        <span class='id identifier rubyid_raise'>raise</span> <span class='const'><span class='object_link'><a href=".