[mq]: smallfixes
diff --git a/apiclient/discovery.py b/apiclient/discovery.py
index c54b57f..3e1964c 100644
--- a/apiclient/discovery.py
+++ b/apiclient/discovery.py
@@ -267,6 +267,8 @@
     if type(value) == type('') or type(value) == type(u''):
       return value
     else:
+      if value is None:
+        raise ValueError('String parameters can not be None.')
       return str(value)
   elif schema_type == 'integer':
     return str(int(value))