Hello, when Backpacked is in the development environment it crash the game.

Here's the error :

[18:06:15] [main/FATAL] [mixin/]: Mixin apply failed backpacked.mixins.json:common.PlayerEntityMixin -> net.minecraft.entity.player.PlayerEntity: org.spongepowered.asm.mixin.injection.throwables.InvalidInjectionException Critical injection failure: @Inject annotation on onFallFlying could not find any targets matching 'Lnet/minecraft/entity/player/PlayerEntity;func_71000_j(DDD)V' in net.minecraft.entity.player.PlayerEntity. Using refmap backpacked.refmap.json [PREINJECT Applicator Phase -> backpacked.mixins.json:common.PlayerEntityMixin -> Prepare Injections -> -> handler$zzi000$onFallFlying(DDDLorg/spongepowered/asm/mixin/injection/callback/CallbackInfo;)V -> Parse]
org.spongepowered.asm.mixin.injection.throwables.InvalidInjectionException: Critical injection failure: @Inject annotation on onFallFlying could not find any targets matching 'Lnet/minecraft/entity/player/PlayerEntity;func_71000_j(DDD)V' in net.minecraft.entity.player.PlayerEntity. Using refmap backpacked.refmap.json [PREINJECT Applicator Phase -> backpacked.mixins.json:common.PlayerEntityMixin -> Prepare Injections -> -> handler$zzi000$onFallFlying(DDDLorg/spongepowered/asm/mixin/injection/callback/CallbackInfo;)V -> Parse]

What should I do to prevent this and continue my addon ^^' ?

In your build.gradle add this to client and server runs.

property 'mixin.env.disableRefMap', 'true'
property 'mixin.env.refMapRemappingFile', "${projectDir}/build/createSrgToMcp/output.srg"

then regen your runs.