title: Regex how can I check that message isn't empty
body: <p>How can I check if a string isn't empty using regex? For example, if the user give a lot of space characters whitout letters, it will be considered as empty</p>
  
  <p>I've tried <code>[a-zA-Z0-9]</code> to check if there's a letter in the string, but this don't work.</p>