Task 5/5 - 'NoneType' is not iterable but works correctly in workspaces

# The dictionary will look something like:
# {'Andrew Chalkley': ['jQuery Basics', 'Node.js Basics'],
#  'Kenneth Love': ['Python Basics', 'Python Collections']}
#
# Each key will be a Teacher and the value will be a list of courses.
#
# Your code goes below here.
def num_teachers(teachers):
    return len(teachers.keys())

def num_courses(courses):
    count = 0
    for course in courses.values():
        for item in course:
            count += 1
    return count

def courses(courses):
    new_list = []
    for course in courses.values():
        for item in course:
            new_list.append(item)
    return new_list

def most_courses(arg):
    max_count = 0
    teachers = " "
    for teacher, listOfCourses in arg.items():
        if len(listOfCourses) > (max_count):
            max_count = len(listOfCourses)
            teachers = teacher
    return teachers

def stats(a_dict):
    new_list = []
    for teacher in a_dict.keys():
        num_courses = len(a_dict[teacher])
        new_list.append([teacher, num_courses])
    print(new_list)