I am not sure if anyone else is having this issue or not, but I can not do in-line attribute compares to null. For instance..... when ObjectA( objectBKey == null ) then .... objectBKey is a String in this case. This doesn't evaluate properly as the rule was firing even though the slot contained the key of ObjectB. Then I did this as a test.... when ObjectA( $objBKey : objectBKey ) not ObjectB( objectBKey == $objBKey ) then ..... This works because if the slot is populated there must be an ObjectB in the system with that unique key. If the $objBKey is null then there obviously is not an ObjectB in the system. I tried searching through the archieve but couldn't find anything for this issue. Also for what it's worth I'm using the official 4.0.5 release. Thanks in advance! Joshua -- View this message in context: http://www.nabble.com/Issues-when-comparing-attribute-values-to-null-tp16... Sent from the drools - user mailing list archive at Nabble.com.