Unable to access properties of document in a list from automation scripting

If an Automation Script is configured to accept documents as the input, I am unable to access properties of individual documents without calling getPropertyValue(). For example, this does not work:

  var creator = input[0]['dc:creator'];

But this does work:

  var creator = input[0].getPropertyValue('dc:creator');

If, on the other hand, I call an Automation Script that is configured to accept document both examples work as expected (removing the array accessor of course).

I will provide a reproducible example.