title: Angular6 Material6 Error: "There can only be one default row without a when predicate function."
body: <p>I'm trying to implement the <code>Table with expandable rows</code> from <a href="https://material.angular.io/components/table/examples" rel="noreferrer">https://material.angular.io/components/table/examples</a> but I get this error:</p>
  
  <p><code>There can only be one default row without a when predicate function.</code></p>
  
  <p>This error comes from the fact that I have two <code>&lt;tr mat-row ...</code>, both without a when predicate (as per example). If I remove one, then the error disappears.</p>
  
  <p>From my own investigation I've found that this feature is new to Material. I upgraded to @angular/material@latest and @angular/cdk@latest and I still got the error.</p>
  
  <p><strong>Does anyone know what I have to do to implement the table as in the example from documentation? <a href="https://material.angular.io/components/table/examples" rel="noreferrer">https://material.angular.io/components/table/examples</a></strong></p>
  
  <p>My versions:</p>
  
  <pre><code>Angular CLI: 6.0.8
  Node: 8.11.2
  OS: win32 x64
  Angular: 6.0.4
  ... animations, common, compiler, compiler-cli, core, forms
  ... http, language-service, platform-browser
  ... platform-browser-dynamic, router
  
  Package                           Version
  -----------------------------------------------------------
  @angular-devkit/architect         0.6.8
  @angular-devkit/build-angular     0.6.8
  @angular-devkit/build-optimizer   0.6.8
  @angular-devkit/core              0.6.8
  @angular-devkit/schematics        0.6.8
  @angular/cdk                      6.3.1
  @angular/cli                      6.0.8
  @angular/flex-layout              6.0.0-beta.16
  @angular/material                 6.3.1
  @ngtools/webpack                  6.0.8
  @schematics/angular               0.6.8
  @schematics/update                0.6.8
  rxjs                              6.2.0
  typescript                        2.7.2
  webpack                           4.8.3
  </code></pre>