title: error TS2345: Argument of type 'X' is not assignable to parameter of type 'X[]'
body: <p>Currently, there is a strange behaviour when trying to create a new object in Typescript. There are two classes:</p>
  
  <pre><code>export class SkaterDrawn {
  
      private ID;
      private name;
      ...
  
  constructor(input?:any) {
      this.ID = input.ID;
      ...
  }
  
  
  export class SkaterDrawnTeam extends SkaterDrawn {
      private skaters:SkaterDrawn[];
  
      constructor(skaters:SkaterDrawn[]) {
          super(skaters[0]);
          this.skaters = skaters;
      }
      ...
  }
  </code></pre>
  
  <p><code>this.registeredSkaters</code> contains an array of elements of type <code>SkaterDrawn</code>. Now I'm grouping this array into an array of chunks, like this:</p>
  
  <pre><code>this.registeredSkaters = this.registeredSkaters.groupBy('teamID');
  this.registeredSkaters = Object.values(this.registeredSkaters);
  </code></pre>
  
  <p>This outputs:</p>
  
  <pre><code>[
      [SkaterDrawn,SkaterDrawn,SkaterDrawn],
      [SkaterDrawn,SkaterDrawn,SkaterDrawn],
      [SkaterDrawn,SkaterDrawn,SkaterDrawn]
  ]
  </code></pre>
  
  <p>Now I'm trying to create a new Object out of this:</p>
  
  <pre><code>let teams = this.registeredSkaters.map((item:SkaterDrawn[]) =&gt; 
      new SkaterDrawnTeam(item);
  })
  </code></pre>
  
  <p>I expected to get an array of <code>SkaterDrawnTeam</code>, but the compilation fails with</p>
  
  <pre><code>ERROR in src/app/competition/components/drawing/drawing.component.ts(166,30): 
  error TS2345: Argument of type 'SkaterDrawn' is not assignable to parameter of type 'SkaterDrawn[]'.
  Type 'SkaterDrawn' is missing the following properties from type 'SkaterDrawn[]': length, pop, push, concat, and 35 more.
  </code></pre>
  
  <p><code>Line 166,30</code> is the line where I try to do <code>new SkaterDrawnTeam(item)</code> I don't know why this fails. What am I doing wrong and how can I fix it?</p>
  
  <p>Thx so much for your help.</p>