example:

rule "This generates an NPE"
when
result : ReservedWordNPEFact(data < 15)
then
result.setData(new Integer(1));
end

At least in the eclipse IDE, this generates an NPE. Change result to something like:

rule "This generates an NPE"
when
f: ReservedWordNPEFact(data < 15)
then
f.setData(new Integer(1));
end

and it goes away.