presto-main/src/main/java/io/prestosql/metadata/PolymorphicScalarFunction.java/PolymorphicScalarFunction/getNullAwareContainerType
class PolymorphicScalarFunction:    private static Class<?> getNullAwareContainerType(Class<?> clazz, boolean nullable)
    {
        if (nullable) {
            return Primitives.wrap(clazz);
        }
        return clazz;
    }