title: Can the conversion of a String to Data with UTF-8 encoding ever fail?
body: <p>In order to convert a <code>String</code> instance to a <code>Data</code> instance in Swift you can use <code>data(using:allowLossyConversion:)</code>, which returns an optional <code>Data</code> instance.</p>
  
  <p>Can the return value of this function ever be <code>nil</code> if the encoding is UTF-8 (<code>String.Encoding.utf8</code>)?</p>
  
  <p>If the return value cannot be <code>nil</code> it would be safe to always force-unwrap such a conversion.</p>