fix to support legacy plugins specs monkeypatching pipelines

logstash-core/lib/logstash/pipeline.rb

@@ -212,7 +212,7 @@ module LogStash; class Pipeline
     signal = false
     batch_size.times do |t|
       event = (t == 0) ? @input_queue.take : @input_queue.poll(batch_delay)
-      
+
       if event.nil?
         next
       elsif event == LogStash::SHUTDOWN || event == LogStash::FLUSH
@@ -255,16 +255,18 @@ module LogStash; class Pipeline
     outputs_events = batch.reduce(Hash.new { |h, k| h[k] = [] }) do |acc, event|
       # We ask the AST to tell us which outputs to send each event to
       # Then, we stick it in the correct bin
-      output_func(event).each do |output|
-        acc[output] << event
-      end
+
+      # output_func should never return anything other than an Array but we have lots of legacy specs
+      # that monkeypatch it and return nil. We can deprecate  "|| []" after fixing these specs
+      outputs_for_event = output_func(event) || []
+
+      outputs_for_event.each { |output| acc[output] << event }
       acc
     end
+
     # Now that we have our output to event mapping we can just invoke each output
     # once with its list of events
-    outputs_events.each do |output, events|
-      output.multi_receive(events)
-    end
+    outputs_events.each { |output, events| output.multi_receive(events) }
   end
 
   def set_current_thread_inflight_batch(batch)