def excluding_vat_price(price):
    vatPrice = ((price * 15) / 115)
    priceWithoutVat = price - vatPrice
    return -1 if price == 0 else round(priceWithoutVat, 2)

Traceback (most recent call last):
  File "tests.py", line 14, in <module>
    test.assert_equals(excluding_vat_price(None), -1)
  File "/workspace/default/solution.py", line 5, in excluding_vat_price
    vatPrice = ((price * 15) / 115)
TypeError: unsupported operand type(s) for *: 'NoneType' and 'int'