Excluding a field from being indexed

Hi,
I've been playing with Spring Data Elasticsearch and it is working well. However I can't seem to tell it not to index a field using the @Field annotation and keep getting the following error:

: object mapping for [xxx] tried to parse field [yyy] as object, but got EOF, has a concrete value been provided to it?

The field is a byte[] and I was hoping to get it ignore this field and get a data from another field, which is base64 encoded.

Any thoughts

Thanks

Can we see the mapping you are using for this?