In the simple test case below, Message is an instantaneous event (i.e. duration = 0) with a list of destinations.
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declare Message
@role( event )
@timestamp(start)
@duration(duration)
end

rule "Hello World"
when
m : Message( status == Message.HELLO, $myMessage : message, $destinations : dest)
$s : String() from $destinations
then
System.out.println( "Dear " + $s + " : >>> " + $myMessage );
end
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if the engine is configured to work in STREAM mode, the output is
Dear NULL :>>> Hello World
...
since the Strings extracted from the Collection "dest" have already been retracted by
the time the rule is fired, following the retraction of the Message event.
The problem does not show in CLOUD mode.