title: Rails validation required numericality even though presence is not set to true
body: <p>I'm trying to save a record which doesn't have one field set -- which has a validate numericality in the models. Even though the presence is not required in the validation, it's still throwing an error that the field is not a number.</p>
  
  <p><strong>Validation:</strong></p>
  
  <pre><code>validates :network_id,    :numericality =&gt; true
  </code></pre>
  
  <p><strong>Code to that is saving model:</strong></p>
  
  <pre><code>networks.each do |network|
    network.url = network.raw_data.link
    network.save!
  end
  </code></pre>
  
  <p><strong>Error:</strong></p>
  
  <pre><code>Validation failed: Network is not a number
  </code></pre>