title: Parse String to Double with null values
body: <p>I have to convert Strings to Doubles, but may be I have a null value. Does it work with <code>Double.parseDouble(stringValue)</code> or <code>Double.valueOf(stringValue)</code>?</p>
  
  <p>What is the difference between this two methods?</p>
  
  <p>Thank you in advance.</p>