title: Rails 3 Actionmailer - How to send only if email exists
body: <p>I have a Rails 3 app sending emails to multiple (2) recipients.  The first recipient is required, but the second is not required.  I get an error if the second recipient is null.  How do I bypass the secondary email if null without getting an error?</p>
  
  <pre><code>  def email_approvers(invoice)
      @subject          = 'Invoice Approval Request'
      @body["invoice"]  = invoice
      @recipients       = invoice.approver_email, invoice.alternate_approver_email
      @from             = "..."
      @sent_on          = Time.now
      @headers          = {}    
    end
  </code></pre>