When retrieving a Concept by the uuid in a GET call like this:
throws org.codehaus.jackson.map.JsonMappingException: Conflicting getter definitions for property \"set\": org.openmrs.Concept#isSet(0 params) vs org.openmrs.Concept#getSet(0 params)
This is because Jackson tries to deserialize the object to a JSON and then finds two methods for the set property (viz. getSet and isSet). Thus, the concept cannot be retrieved.
One suggested way to solve this is to disable auto-detection of is getters. http://wiki.fasterxml.com/JacksonFeaturesSerialization