fix few more flake8 warnings

Author: worried-networking

plexapi/library.py

@@ -378,13 +378,13 @@ def get(self, title):
         return self.fetchItem(key, title__iexact=title)
 
     def all(self, sort=None, **kwargs):
-        """ Returns a list of media from this library section. 
-        
+        """ Returns a list of media from this library section.
+
             Parameters:
                     sort (string): The sort string
         """
         sortStr = ''
-        if sort != None:
+        if sort is not None:
             sortStr = '?sort=' + sort
 
         key = '/library/sections/%s/all%s' % (self.key, sortStr)