title: Scala add to empty map
body: <p>I have a mutable Map in a List like so:</p>
  
  <pre><code>val aListMap = List(Map[StringType, Any])
  </code></pre>
  
  <p>I want to add key-val pairs to the map like:</p>
  
  <pre><code>aListMap(0) += ("aKey", "anElem")
  </code></pre>
  
  <p>I'm getting <code>Type mismatch: expected String, actual: (String, String)</code>. Is there a different syntax to do this?</p>