NPE when mapping nested entity that is not @Indexed but has @Field

This comes from the C# testsuite, a cache is created with the following template:

  <distributed-cache name="queryCache">
   <indexing>
     <indexed-entities>
<indexed-entity>sample_bank_account.User</indexed-entity>
<indexed-entity>sample_bank_account.Transaction</indexed-entity>
</indexed-entities>
</indexing>
</distributed-cache>

protobuf schema bank.proto is attached.
When trying to put an entry into the cache with the protobuf marshaller an exception is raised. See attach exeception.log

same test works in 11.0.9