From b19e0831655763e7143ebee37655648904e970ec Mon Sep 17 00:00:00 2001
From: der-stefan <stefan_erhardt@gmx.de>
Date: Thu, 2 Jan 2014 06:17:31 -0800
Subject: [PATCH] Add hint to NULL query

---
 Filter.md | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/Filter.md b/Filter.md
index c7f3413..6e01c68 100644
--- a/Filter.md
+++ b/Filter.md
@@ -21,12 +21,17 @@ And they can be combined in complex rules using brackets: `(` and `)`.
 Attributes can be compared against [Regular expressions](http://en.wikipedia.org/wiki/Regular_expression) using the `.match` operator.
 
 ## Examples in XML
-Matches all Objects that have an attribute "amenity" with a value of "restaurant":
+Matches all objects that have an attribute "amenity" with a value of "restaurant":
 
 ```xml
     <Filter>[amenity] = 'restaurant'</Filter> 
 ```
 
+Match if a value is NULL:
+```xml
+    <Filter>[amenity] = 'restaurant' and not ([name] = null)</Filter> 
+```
+
 NEW in Mapnik 2.1.x: Matches all features that contain point geometries:
 
 ```xml