basho/riak-java-client — pull request #137 by guidomedina (2012-05-31 15:14:08+00:00)
Title: @RiakIndex annotation only supports String or Integer field

Added support for collection on indexes on Fields and Methods with collection types restricted to Set or Set or subclasses. One way indexes when using @RiakIndex at the method level since it is expected to be a calculated index (in the case you want to fetch the index value back you have to do at the Field level)