Permgen leak when doing Import All if a Plugins2 Webwork Action plugin is loaded

JiraSafeActionParameterSetter holds a Map<Class<? extends Action>, PropertyDescriptor[]> to cache the action class's checked parameter lookup. The key in this class is a strong reference, and the class itself is held for the lifetime of the application by WebWork.

The key in this map needs to be a weak reference, not a strong one.