code: public <T, K> JacksonDBCollection<T, K> getReferenceCollection(String collectionName, JavaType type, JavaType keyType) {
          return getReferenceCollection(new JacksonCollectionKey(collectionName, type, keyType));
      }
docs: Get a collection for loading a reference of the given type
  
  @param collectionName The name of the collection
  @param type           The type of the object
  @param keyType        the type of the id
  @return The collection