title: Can't construct a query for the property, since the query selector wasn't defined
body: <p>Currently have this problem with a component in Angular 2 that exists of other components. The components of the 'main' component can exist multiple times in the hierarchy.</p>
  
  <p>But i am getting this error:
  <strong>"Can't construct a query for the property "navComponent" of "SidenavLinkComponent" since the query selector wasn't defined"</strong></p>
  
  <pre><code>SidenavLinkComponent:
  @ContentChild(SidenavNavComponent) navComponent: SidenavNavComponent;
  
  SidenavNavComponent:
  @ContentChildren(SidenavLinkComponent) linkComponents: QueryList&lt;SidenavLinkComponent&gt;;
  </code></pre>
  
  <p>I have made this slim plunker, where the problem is shown:
  <a href="https://plnkr.co/edit/Dnpmv6X2IO3WGQAg0372?p=preview" rel="noreferrer">Plunker</a></p>
  
  <p>I have no idea why it happens.</p>