title: regular expression for anything but an empty string
body: <p>Is it possible to use a regular expression to detect anything that is NOT an "empty string" like this:</p>
  
  <pre><code>string s1 = "";
  string s2 = " ";
  string s3 = "  ";
  string s4 = "   ";
  </code></pre>
  
  <p>etc.</p>
  
  <p>I know I could use trim etc. but I would like to use a regular expression.</p>