title: How to delete with Firebase's updatechildvalues in Swift 3?
body: <p>Setting the value of a key to nil results in that key value pair being deleted from the system.  In a certain context, I need to update one key with a legit value, and delete a different key value pair.  I need a guarantee for either both of these transactions to run, or neither of them to run, hence the necessity to use update value.  However I have a problem, update value takes a dictionary, and as we all know setting a dictionary's key to nil results in that key value pair being absent from the dictionary (contrary to what firebase's docs allude to).  So how can I accomplish my goal?</p>
  
  <pre><code>ref.updateChildValues([path1 : realValue, path2 : nil])
  </code></pre>
  
  <p>The above code results in value at path1 being updated, but value at path2 is never deleted.  Any help is greatly appreciated!</p>