[rules-users] using null in drools rulebase

hi everyone need a bit more help here. im currently attempting to write some rules into my rulesbase and can't seem to get the system to check if a variable is empty. i have tried using null as shown in the code below rule "small beak + small body + garden" when Beak(beak == "small beak", beak = null) && Body(body == "small body") Location(location == "garden") then ES.resultsmx("<p> ); ES.resultsmx( Robin </p>"); ES.resultsop(); end which dosent work but for some reason i am able to check if it is not null by doing this rule "small beak + small body + garden" when Beak(beak == "small beak", beak != null) && Body(body == "small body") Location(location == "garden") then ES.resultsmx("<p> ); ES.resultsmx( Robin </p>"); ES.resultsop(); end I have tired using == null but this returns a false and the rule dosent run. can anyone help me please. Also if anyone has any knowledge of how to write rules so it only outputs one result instead of repeatedly running the conditions and outputting results for each correct condition and also how to check if a string variable contains a substring (within a rule) that would be greatly appreciated . Thanks in advance mike -- View this message in context: http://www.nabble.com/using-null-in-drools-rulebase-tf3244300.html#a9018648 Sent from the drools - user mailing list archive at Nabble.com.