Challange task 4 of 4 appears bugged, "'Nonetype' has no len()" error

# The dictionary will be something like:
# {'Jason Seifer': ['Ruby Foundations', 'Ruby on Rails Forms', 'Technology Foundations'],
#  'Kenneth Love': ['Python Basics', 'Python Collections']}
#
# Often, it's a good idea to hold onto a max_count variable.
# Update it when you find a teacher with more classes than
# the current count. Better hold onto the teacher name somewhere
# too!
#
# Your code goes below here.
def most_classes(myDict):
  winrarTeacher = ""
  winrarClasses = 0
  for teacher in myDict.keys():
    numClasses = len(myDict[teacher])
    if numClasses > winrarClasses:
      winrarTeacher = teacher
      winrarClasses = numClasses
    else:
      continue
  return winrarTeacher

def num_teachers(myDict):
  return len(myDict)

def stats(myDict):
  myList = []
  try:
    for item in myDict:
      #myList.append([item, myDict[item]])
      count = 0
      for subItem in myDict[item]:
        count += 1
      myList.append([item,count])
  except:
    fYou = True
  return myList

def courses(myDict):
  allCourses = []
  for item in myDict:
    allCourses.append(myDict[item])