So, the error I'm getting is "Oops, try again. median([1]) resulted in an error: object of type 'NoneType' has no len()" so I would really appreciate some help.

```
def median(lists):
sort_list = lists.sort()
if len(sort_list)% 2 == 0:
middle = len(sort_list)/ 2
middley = sort_list[middle] - 1
median = sort[middle] + sort_list[middley]/ 2
else:
middle = len(sort_list)/2
median = sort_list[middle]
return median
```