Checking the forum, I know my code is correct, but I still get this msg:

Oops, try again. get_class_average([alice]) resulted in an error: 'NoneType' object is not iterable

Code is below. I've been stuck on this for 2 days now. Please give me "the silver bullet"!

```
lloyd = {
"name": "Lloyd",
"homework": [90.0, 97.0, 75.0, 92.0],
"quizzes": [88.0, 40.0, 94.0],
"tests": [75.0, 90.0]
}
alice = {
"name": "Alice",
"homework": [100.0, 92.0, 98.0, 100.0],
"quizzes": [82.0, 83.0, 91.0],
"tests": [89.0, 97.0]
}
tyler = {
"name": "Tyler",
"homework": [0.0, 87.0, 75.0, 22.0],
"quizzes": [0.0, 75.0, 78.0],
"tests": [100.0, 100.0]
}
# Add your function below!
def average(numbers):
total = sum(numbers)
total = float(total)
return total / len(numbers)
def get_average(student):
homework = average(student["homework"])
quizzes = average(student["quizzes"])
tests = average(student["tests"])
return 0.10 * homework + 0.30 * quizzes + 0.60 * tests
a = get_average(lloyd)
b = get_average(alice)
c = get_average(tyler)
print a, b, c
def get_letter_grade(score):
if score >= 90:
return "A"
elif score >= 80 and score < 90:
return "B"
elif score >= 70 and score < 80:
return "C"
elif score >= 60 and score < 70:
return "D"
else:
return "F"
score = get_average(lloyd)
print get_letter_grade(score)
def get_class_average(students):
results = []
for student in students:
results = results.append(get_average(student))
return average(results)
```