Need Help with some crashes

What do java.lang.NullPointerException: Cannot invoke "net.minecraft.world.entity.Entity.setDeltaMovement(net.minecraft.world.phys.Vec3)" because the return value of "java.util.Optional.orElse(Object)" is null, and > Process 'command 'C:\Program Files\Pylo\MCreator\jdk\bin\java.exe'' finished with non-zero exit value -805306369 mean, and how do I fix them?