--- a/pvl/syslog/filter.py	Fri Jan 04 21:27:17 2013 +0200
+++ b/pvl/syslog/filter.py	Fri Jan 04 21:31:21 2013 +0200
@@ -13,7 +13,8 @@
             Match using given { field: regex }.
         """
         
-        self.filters = filters
+        # drop None's
+        self.filters = dict((attr, regex) for attr, regex in filters.iteritems() if regex is None)
 
     def match_prog (self, attr, glob, prog=None) :
         """
@@ -114,3 +115,7 @@
                 yield item
     
     __call__ = process
+
+    def __nonzero__ (self) :
+        return bool(self.filters)
+