Filtering Dictionary in Python 3

erronous_example.py

from typing import Dict

def get_menu() -> Dict[str, dict]:
    return {
        "TIMMY_BLACK": {
            "item": "Timmy's Coffee Barista's Black",
            "sugar_free": True,
            "with_milk": False,
        },
        "TIMMY_LATTE": {
            "item": "Timmy's Coffee Latte",
            "sugar_free": True,
            "with_milk": False,
        },
        "TIMMY_SWEETENED_LATTE": {
            "item": "Timmy's Coffee Latte - Sweetened",
            "sugar_free": True,
            "with_milk": True,
        },
        "TIMMY_SIGNATURE_CARAMEL": {
            "item": "Timmy's Signature - Caramel Latte",
            "sugar_free": None,  # Unknown
            "with_milk": True,
        }
    }

coffees = get_menu()

# Filter unsweetened coffees -> RuntimeError
for code, details in coffees.items():
    if details.get("sugar_free") is True: 
        del coffees[code]