title: Angular Material mat-table not returning any results upon filter
body: <p>I have attempted to re-create a mat-table using the Angular Material package. The mat-table examples have recently been massively improved, which is amazing. They provided this <a href="https://stackblitz.com/angular/rlqmgldaryol" rel="nofollow noreferrer">example here with both sort and filter features</a>.</p>
  
  <p>I have attempted to reproduce this within the context of my own app, using dummy data in a minimal example on stackblitz <a href="https://angular-5nyyrl.stackblitz.io" rel="nofollow noreferrer">here</a>. </p>
  
  <p>The table displays and is populated with data, but as soon as I type more than one letter, the filter method seems to incorrectly be removing all entries, even ones that it should not.</p>
  
  <p>One difference that I can think of here is that in my example, I'm using a class in my declaration of the dataSource: <code>dataSource: MatTableDataSource&lt;Match&gt;;</code>, whereas in the example provided by the Angular people, it's an interface: <code>dataSource: MatTableDataSource&lt;UserData&gt;;</code>.</p>
  
  <p>This is just as likely a red herring, though, as I tried playing with an interface instead with no success. Any help here is very much appreciated.</p>