str operator in 'accumulate', with operand from 'from', results in NPE at KB build ---------------------------------------------------------------------------------- Key: DROOLS-574 URL: https://issues.jboss.org/browse/DROOLS-574 Project: Drools Issue Type: Bug Security Level: Public(Everyone can see) Affects Versions: 6.1.0.Final Reporter: Matteo Mortari Assignee: Mark Proctor Attachments: 20140813.drools6test.strStandardEvInAccumulate.zip This is an exercise for "group by" words. Consider the following pattern for realizing a "group by" by means of from/accumulate/count : the goal is to count Messages which starts with preferred keyword, if the count for a keyword is >= 2, then rule should fire. {code} declare GroupByString groupId : String groups : String[] end rule "init words of my interest" no-loop when then GroupByString grp = new GroupByString(); grp.setGroupId("wordGroup"); grp.setGroups(new String[]{"ciao", "bella"}); insert(grp); end rule "group by word and count if >=2 then " no-loop when $group : GroupByString( groupId == "wordGroup") $word : String() from $group.groups accumulate ( $msg : Message( text str[startsWith] $word ) over window:time( 5m ) ; $list : collectList( $msg ), $count : count( $msg ); $count >= 2 ) then System.out.println("group by " + $word + " count is "+ $count + " list: " + $list); insert(new Integer($count.intValue())); end {code} However trying to compile the KB with the kie-maven-plugin fails with this NPE and stacktrace (snippet): {noformat} java.lang.NullPointerException at org.drools.compiler.rule.builder.dialect.java.JavaAccumulateBuilder.buildExternalFunctionCall(JavaAccumulateBuilder.java:182) at org.drools.compiler.rule.builder.dialect.java.JavaAccumulateBuilder.build(JavaAccumulateBuilder.java:101) at org.drools.compiler.rule.builder.dialect.java.JavaAccumulateBuilder.build(JavaAccumulateBuilder.java:66) at org.drools.compiler.rule.builder.PatternBuilder.build(PatternBuilder.java:320) at org.drools.compiler.rule.builder.PatternBuilder.build(PatternBuilder.java:138) at org.drools.compiler.rule.builder.GroupElementBuilder.build(GroupElementBuilder.java:66) at org.drools.compiler.rule.builder.RuleBuilder.build(RuleBuilder.java:89) at org.drools.compiler.builder.impl.KnowledgeBuilderImpl.addRule(KnowledgeBuilderImpl.java:1652) at org.drools.compiler.builder.impl.KnowledgeBuilderImpl.compileRules(KnowledgeBuilderImpl.java:968) {noformat} I've also noticed the following 2 aspects: 1-/ If you use another operator instead of {{str startsWith}}, for instance you replace with the {{contains}} operators, it does compile the KB successfully. In this scenario would change the exercise to "count Messages which _contains_ the preferred keyword", but it works: {code} rule "group by word and count if >=2 then " no-loop when $group : GroupByString( groupId == "wordGroup") $word : String() from $group.groups accumulate ( $msg : Message( text contains $word ) over window:time( 5m ) ; $list : collectList( $msg ), $count : count( $msg ); $count >= 2 ) then System.out.println("group by " + $word + " count is "+ $count + " list: " + $list); insert(new Integer($count.intValue())); end {code} 2-/ If you use an hard-coded operand in the {{str startsWith}}, it works too. For instance if you hard-code the rule as: {code} rule "group by word and count if >=2 then " no-loop when accumulate ( $msg : Message( text str[startsWith] "ciao" ) over window:time( 5m ) ; $list : collectList( $msg ), $count : count( $msg ); $count >= 2 ) then insert(new Integer($count.intValue())); end {code} It does not give NPE at KB build and executes as expected. For my application it's okay to deal with the first option above, but anyway I thought worthy to report a JIRA. I will attach reproducer. Ciao