fixed can't raise invalid expire time when set ex param is 0

Author: huangqiyin

redis/client.py

@@ -1150,7 +1150,7 @@ def set(self, name, value, ex=None, px=None, nx=False, xx=False):
             already exists.
         """
         pieces = [name, value]
-        if ex:
+        if ex is not None:
             pieces.append('EX')
             if isinstance(ex, datetime.timedelta):
                 ex = ex.seconds + ex.days * 24 * 3600