title: prompt option not working with select_tag
body: <p>If there is value in marital_status then prompt should not be displayed but in my case it's displaying. My code is mentioned below. Please help.</p>
  
  <pre><code>= select_tag( 'request[marital_status]', 
  options_for_select(marital_status_options,
  @employee.marital_status.try(:upcase)), prompt: "Select Marital Status", id: 'employee_marital_status', disabled: @request.submitted?)
  </code></pre>
  
  <p>In employee_helper.rb</p>
  
  <pre><code>def marital_status_options
    Employee::MaritalStatus::ALL.zip(Employee::MaritalStatus::ALL)
  end
  </code></pre>
  
  <p>In employee model</p>
  
  <pre><code>module MaritalStatus
    MARRIED = 'MARRIED'
    SINGLE = 'SINGLE'
    DIVORCED = 'DIVORCED'
    ALL = [MARRIED, SINGLE, DIVORCED]
  end
  </code></pre>