1.16.5 Custom Entity Models causes the Gradle Build to fail

Hi I've ported my mod from 1.17.1 to 1.16.5 and after doing so it created a lot of issues with the mod most of which I have resolved except when I try changing my old 1.17 Mojomaps entity model to 1.15/1.16 Mojomaps and import it causes the gradle to fail with this as its report:

https://pastebin.com/bu8N4tze