Thanks to another forum post (https://forum.liquibase.org/t/includeall-with-v4-0-0/4655 I’ve managed to figure out what’s going on with this issue! Thank you @Joachim!
In the post above Joachim mentioned that there seemed to be a change in 4.0.0 to the way that resources are looked up if they are in a jar file (their issue was with includeAll, which we don’t use in our liquibase setup, but I assumed that it would be a change that affects any resource that the scripts require, including csv files). So based on that I realised that maybe the issue was to do with the fact that changes to csv files don’t automatially trigger a rebuild in Intellij and therefore the csv files in the jar file that liquibase was trying to access were not always the latest versions. I normally run liquibase from within intellij while I’m developing and changes to csv files have always been included when running liquibase in the past.
So basically, to fix this issue all I had to do was to hit the Build button in intellij before running liquibase to make sure that the latest version of the csv files are included in the jar file!
So I can now confirm that liquibase 4.0.0 does actually work for us as long as we change our csv files to include NULL for nullable columns and we build the project in intellij before running in a dev environment.
It would be good if the liquibase developers could provide some details as to exactly how resources are accessed in 4.0.0 and why they made this change, but for now I’m just happy that I finally managed to get 4.0.0 working 