Null string as input

Hi there!

I am trying to set up an input/output test to validate correct handling of empty input (users just pressing ENTER without typing anything), so I added the following test case to the autograding.json file:

      "name": "Test6",
      "setup": "",
      "run": "LANG=en_US.utf8 timeout 3m python3",
      "input": "",
      "output": "'' no comienza con 'A'",
      "comparison": "included",
      "timeout": 1,
      "points": null

But it’s not working. The program just waits for input until it times out and the test case fails.

The input instruction in the program is a simple:

palabra = input("Escribe una palabra: ")

Any ideas on how to set up autograding for empty input?

Edit: I also tried using: "input": null to no avail.