title: Undefined and Null in *NgIf
body: <p>Are <code>null</code>, <code>undefined</code> and <code>&quot;&quot;&lt;empty string&gt;</code> value treated similarly by *Ngif?
  For example, is this:
  <code>*ngIf = &quot;foo == null&quot;</code></p>
  <p>Treated the same as:
  <code>*ngIf = &quot;foo == undefined&quot;</code></p>
  <p>If not, is there a simpler way to use *ngIf to not show properties with the value null, undefined, and &quot;&quot;?</p>