Hi All,

i've a simple rules that retract objects form the WM


rule "Retract From ArrayList"
when
$total: ArrayList() from collect ( PrestationFacturable()  )

then
retract($total.get(0));
end

at the end of fireAll all the fact are well retracted but if I replace ArrayList by TreeSet


rule "Retract From TreeSet"
when
$tree: TreeSet() from collect ( PrestationFacturable()  )

then
retract($tree.first());
end


I got the following exception
org.drools.spi.ConsequenceException: org.drools.FactException: Retract error: handle not found for object: [6, val=1]. Is it in the working memory?

because the $tree (at second run) still contains the object that as been removed 


can somebody can explain this behavior ?


Thanks in advance

-P.