Pete

Using the plugin from a multi branch pipeline with a number of parallel stages, the following has been observed sporadically. ``` java.util.ConcurrentModificationException at java.util.HashMap$HashIterator.nextNode(HashMap.java:1445) at java.util.HashMap$KeyIterator.next(HashMap.java:1469) at com.thoughtworks.xstream.converters.collections.CollectionConverter.marshal(CollectionConverter.java:73) at com.thoughtworks.xstream.core.AbstractReferenceMarshaller.convert(AbstractReferenceMarshaller.java:69)...