The aggregation was working fine before the spring boot version upgrade. After upgrading to 2.5.14, I'm facing issue with MongoTemplate.aggregate(Aggregation aggregation, Class<?> inputType, Class outputType) as :
org.springframework.data.mapping.MappingException: Cannot convert [] of type class java.util.ArrayList into an instance of class java.lang.String! Implement a custom Converter<class java.util.ArrayList, class java.lang.String> and register it with the CustomConversions.