python: Fix the remaining broken NULL pointer tests

Signed-off-by: Justus Winter <4winter@informatik.uni-hamburg.de>

bindings/python/notmuch/database.py

@@ -558,7 +558,7 @@ class Database(object):
         """
         self._assert_db_is_initialized()
         tags_p = Database._get_all_tags(self._db)
-        if tags_p == None:
+        if not tags_p:
             raise NullPointerError()
         return Tags(tags_p, self)
 

bindings/python/notmuch/message.py

@@ -229,7 +229,7 @@ class Message(Python3StringMixIn):
 
         #Returns NULL if any error occurs.
         header = Message._get_header(self._msg, _str(header))
-        if header == None:
+        if not header:
             raise NullPointerError()
         return header.decode('UTF-8', 'ignore')
 
@@ -300,7 +300,7 @@ class Message(Python3StringMixIn):
             raise NotInitializedError()
 
         tags_p = Message._get_tags(self._msg)
-        if tags_p == None:
+        if not tags_p:
             raise NullPointerError()
         return Tags(tags_p, self)
 

bindings/python/notmuch/messages.py

@@ -142,7 +142,7 @@ class Messages(object):
         #reset _msgs as we iterated over it and can do so only once
         self._msgs = None
 
-        if tags_p == None:
+        if not tags_p:
             raise NullPointerError()
         return Tags(tags_p, self)
 

bindings/python/notmuch/thread.py

@@ -238,7 +238,7 @@ class Thread(object):
             raise NotInitializedError()
 
         tags_p = Thread._get_tags(self._thread)
-        if tags_p == None:
+        if not tags_p:
             raise NullPointerError()
         return Tags(tags_p, self)