title: Creating Extension method of 'Any' Type. Error: 'Any' only refers to a type, but is being used as a value here
body: <p>I want to create extension method that of ANY type that takes string or number if It is NAN or NULL convert it to empty string But getting this error .</p>
  <pre><code>
  declare global {
      interface Any {
          NullToEmptyString(): any;
      }
  }
  
  Any.prototype.NullToEmptyString = function (): any{ &lt;--- Here is error
      return this == null ? '' : this;
  }
  </code></pre>