title: Serialize Array[Array[Byte]] to Json
body: <p>I'm having an Array[Array[Byte]] and I would like to serialize it to Json in Playframework:</p>
  
  <pre><code>implicit val matrixWrites = new Writes[matrix] {
      def writes(c: Matrix): JsValue = {
    Json.obj(
          "id" -&gt; c.id,
          "matr" -&gt; c.matr
        )
      }
    }
  </code></pre>
  
  <p>However I get the error <code>Type mismatch: found (String, Array[Array[Byte]] required (String, Json.JsValueWrapper)</code> </p>
  
  <p>What is the correct way to turn a Array[Array[Byte]] into Json?</p>