title: C# dictionaries ValueOrNull / ValueorDefault
body: <p>Currently I'm using</p>
  
  <pre><code>var x = dict.ContainsKey(key) ? dict[key] : defaultValue
  </code></pre>
  
  <p>I'd like some way to have dictionary[key] return null for nonexistant keys, so I could write something like</p>
  
  <pre><code>var x =  dict[key] ?? defaultValue;
  </code></pre>
  
  <p>this also winds up being part of linq queries etc. so I'd prefer one-line solutions. </p>