title: Replacing null String to empty String
body: <p>I have a small problem, but it's hard for me to solve it.</p>
  
  <p>I have built a String that is a collection of some object's attributes, constructed and delimited by <code>||</code>. But whenever I have some <code>null</code> attribute, it keeps on printing <code>null</code>, I want to replace <code>null</code> with empty string.</p>
  
  <p>For example, for the input</p>
  
  <pre><code>ADS||abc||null||null
  </code></pre>
  
  <p>I want it to become</p>
  
  <pre><code>ADS||abc||||
  </code></pre>
  
  <p>I tried these two, but they didn't work:</p>
  
  <pre><code>string.replace(null,"")
  string.replace("null","")
  </code></pre>
  
  <p>Can someone please help?</p>