fixed issue 1147, belongs(None), thanks Marin

VERSION

@@ -1 +1 @@
-Version 2.2.1 (2012-11-06 10:36:39) stable
+Version 2.2.1 (2012-11-06 14:26:21) stable

gluon/dal.py

@@ -1199,7 +1199,7 @@ class BaseAdapter(ConnectionPool):
     def BELONGS(self, first, second):
         if isinstance(second, str):
             return '(%s IN (%s))' % (self.expand(first), second[:-1])
-        elif second==[] or second==():
+        elif not second:
             return '(1=0)'
         items = ','.join(self.expand(item, first.type) for item in second)
         return '(%s IN (%s))' % (self.expand(first), items)