This has been bothering me (and likely many other users) since its introduction in #57

It used to be that the event.set(xpath_dest, data) was protected by existing after the return if value.is_a?(Array) && value.length == 0 (which is now a next) and within the normalized_nodeset.each loop

Now, data is initialized and event.set(xpath_dest, data) occurs regardless of what happens within the loop. The result is empty event fields being set where in the past, nothing would be set.

The repercussions are pretty significant for anyone relying on xml xpath results for subsequent filter plugins e.g. geoip

So far this change has forced me to use methods similar to this literally anytime I dare to use xml and the cost is unnecessary.

ruby {
    code => "event.remove('FieldName') if event.get('[FieldName]').empty?"
}

No testing has been been performed on this change (except for the included rspec test which is passing), however given the above explanation the logic is pretty straight forward.
e.g.

force_array = false
data = []

if data.size == 1 && !force_array
    puts true
else
    puts false unless data.empty?
end

^ shouldn't return anything

Solves #61