Already picking up the necessary Jackson modules. No need to register the internal one twice.

spring-data-rest-webmvc/src/main/java/org/springframework/data/rest/webmvc/RepositoryAwareMappingHttpMessageConverter.java

@@ -62,7 +62,7 @@ public class RepositoryAwareMappingHttpMessageConverter
   }
 
   @Override public void afterPropertiesSet() throws Exception {
-    mapper.registerModule(jacksonModule);
+    //mapper.registerModule(jacksonModule);
     for(Module m : modules) {
       mapper.registerModule(m);
     }