When making a procedure for a sapling to check if the block it is on is grass or dirt the program is fine. Once you load into a world and place the sapling though, the game crashes immediately. There really isn't anything more too it than that.
MCreator issue tracker has been migrated to GitHub.
Existing tickets have been migrated to GitHub. Please open new tickets on the GitHub tracker instead. If you do not have a GitHub account, all feature requests and bug reports from forums are still considered and checked by the maintainers.