Problems with select

Rails
1

Hello to every bofy i’m working with Ruby and i havve the next problem
when i want to select an option from a select.

I have the next code:

<p>
  <%= f.label :es_pyme, I18n.t('tog_user.model.es_pyme') %>
<select name="user[es_pyme]" class="fieldbox">
      <option value= "" >
          <%= I18n.t("tog_user.model.select_type_of_user") %>
        </option>
    <option value= "Usuario" > Usuario </option>
    <option value= "Pyme" > Pyme </option>
</select>
</p>

and in my model

validates_presence_of :es_pyme

and when i select an option always appear that es_pyme is null.

Which is the problem?

thanks and greetings.