Mcreator not running test minecraft

So, I'm happily modding, when I try and run client. It starts up the FML early loading process, then finishes and Minecraft doesn't open. I see it open in the taskbar but it closes instantly. I check Console and BUILD FAILED is there in red. I see something about deprecated gradle features being incompatible with Gradle 5.0, and something ending up with -1 when it shouldn't be. Help please! Without test client I can't test my mod and I really don't want to release something possibly broken to the community.