There are some REST methods (PolicyController#getCorrelationRuleClasses or TaskController#getJobClasses) returning Set<String> containing the names of classes implementing a specific interface.
Such methods are called by the admin console, for example, when defining a new policy or a new task.
In case there are no custom implementation provided (this happens for SyncRule, currently), an exception is logged:
org.codehaus.jackson.map.JsonMappingException: Can not deserialize instance of MyObject out of START_ARRAY token
This problem does not affect CXF services since in that case the class names are wrapped in specific transfer objects.