title: Default value in dart Map
body: <p>Is there a way to get a default value from a Map in dart (like Java):</p>
  
  <pre><code>static Map DEFAULT_MAPPING = Map.unmodifiable({
      "k1": "value"
  });
  
  DEFAULT_MAPPING['k1'] //get 'value'
  
  DEFAULT_MAPPING.getOrElse('non-present-key', 'default-value') //something like Java has
  </code></pre>