--- a/bin/pvl.hosts-dhcp	Thu Dec 19 18:50:59 2013 +0200
+++ b/bin/pvl.hosts-dhcp	Thu Dec 19 18:58:15 2013 +0200
@@ -19,7 +19,10 @@
     yield "}"
 
 def dhcp_quote (value) :
-    return '"{value}"'.format(value=value)
+    if value is None :
+        return None
+    else :
+        return '"{value}"'.format(value=value)
 
 def process_host (options, host) :
         if host.owner :