title: Typescript Interface with nullable properties
body: <p>I have an interface <em>IFilterSet</em>  with nullable fields:</p>
  
  <pre><code>export interface IFilterSet {
          filter1?: boolean;
          filter2?: boolean;
          filter3?: number;
          fitler4?: string;
      }
  </code></pre>
  
  <p>I receive another <em>object X</em>, that <strong>may</strong> contain IFilterSet object among others.</p>
  
  <p>I want to map the IFilterSet properties of object X. 
  First quess would be to make a loop for those properties, but because they are nullable, it won't work, there will be nothing to loop through.
  Initialiazing an empty IFilterSet would defeat the purpose of those properties being nullable, right?</p>