title: Angular 4, Conditional display with ngIf
body: <p>help to fix condition to display data.
  I get model of M through async service, so i use >model?.something&lt; notation to avoid errors when model is still undefined. title is null or 'somestring'.
  Something wrong with expression. Whatever form i choose it always display one of cases.
  I have avoided this type expression early and can not translate correctly to typescript.</p>
  
  <pre><code>import { Component } from '@angular/core';
  import { M } from './model';
  
  @Component({
    selector: 'app-test',
    template: `
  &lt;p *ngIf="model1?.title !== null"&gt;
    Display text if title exist('common string')
  &lt;/p&gt;
  &lt;p *ngIf="model2?.title === null"&gt;
    Display text if title equal to null
  &lt;/p&gt;
    `,
    styleUrls: ['./test.component.css']
  })
  
  export class TestComponent {
    model1: M;
    model2: M;
    constructor() {
      this.model1 = {
        title: 'username'
      };
      this.model2 = {
        title: null
      };
    }
  }
  
  export class M {
      public title: string;
  
      public constructor(){}
  }
  </code></pre>