title: NullReferenceException was unhandled C#
body: <p>Visual Studio 2010 - (Windows Forms) in C#</p>
  
  <p>I have this code:</p>
  
  <pre><code>private void cbxValuta_SelectedIndexChanged(object sender, EventArgs e)
      {
          try
          {
              string primo = cbxValuta.SelectedItem.ToString();
              string secondo = cbxValuta2.SelectedItem.ToString();
              double cambio = double.Parse(CurrencyConverter.Convert(1.0m, primo, secondo));
              tbxConvertito.Text = (double.Parse(tbxDaConvertire.Text) * cambio).ToString();
  </code></pre>
  
  <p>I get this error:</p>
  
  <blockquote>
    <p>NullReferenceException was unhandled
    Object reference not set to an instance of an object.</p>
  </blockquote>
  
  <p>How Can I solve this issue?</p>