title: Null aware function invocation operator
body: <p>In the same way we can have </p>
  
  <pre class="lang-dart prettyprint-override"><code>nullableClassInstance?.method(blah)
  </code></pre>
  
  <p>Is there a way to do</p>
  
  <pre class="lang-dart prettyprint-override"><code>nullableFunctionInstance?(blah)
  </code></pre>
  
  <p>In other words, is there an operator that checks whether a function instance is not <code>null</code>, if so, invoke the function all in one line?</p>