code: public static Builder builder(ReduceFunction udf, Class<? extends Key<?>> keyClass, int keyColumn) {
  		return new Builder(new UserCodeObjectWrapper<ReduceFunction>(udf), keyClass, keyColumn);
  	}
docs: Creates a Builder with the provided {@link ReduceFunction} implementation.
  
  @param udf The {@link ReduceFunction} implementation for this Reduce contract.
  @param keyClass The class of the key data type.
  @param keyColumn The position of the key.