title: Assignment operation that does nothing if variable is null?
body: <p>I want to conditionally assign a value to a variable if that variable is already <code>null</code>. Furthermore, if that variable is not already <code>null</code> I want <strong>nothing</strong> to occur and I want to be able to do all with a single operator.</p>
  
  <pre><code>object a = null;
  object b = new Something();
  
  // this is essentially what I want but done with an operator:
  if(a == null)
  {
      a = b;
  }
  
  // this is all I feel I have to work with,
  a = a || b;
  a = a ?? b;
  a = a == null ? b : a;
  
  // the above methods all end up performing a = a if a is not null
  </code></pre>