code: public <H,R> Map<String,AttributeValue> convertKey(final T key) {
          final DynamoDBMapperFieldModel<T,H> hk = this.<H>hashKey();
          final DynamoDBMapperFieldModel<T,R> rk = this.<R>rangeKeyIfExists();
          return this.<H,R>convertKey(hk.get(key), (rk == null ? (R)null : rk.get(key)));
      }
docs: Creates a new key map from the specified object.
  @param <H> The hash key type.
  @param <R> The range key type.
  @param object The object instance.
  @return The key map.