presto-main/src/main/java/io/prestosql/operator/aggregation/AccumulatorCompiler.java/AccumulatorCompiler/generatePrepareFinal
class AccumulatorCompiler:    private static void generatePrepareFinal(ClassDefinition definition)
    {
        MethodDefinition method = definition.declareMethod(
                a(PUBLIC),
                "prepareFinal",
                type(void.class));
        method.getBody().ret();
    }