Can you help me pls

The server rift use mixin of sponge powered but crash i don’t know the causes and give this error:
ixin apply failed mixins.rift.core.json:MixinMinecraftServer → net.minecraft.server.MinecraftServer: org.spongepowered.asm.mixin.transformer.throwables.InvalidMixinException Shadow field r was not located in the target class net.minecraft.server.MinecraftServer. Using refmap mixins.rift.refmap.json
org.spongepowered.asm.mixin.transformer.throwables.InvalidMixinException: Shadow field r was not located in the target class net.minecraft.server.MinecraftServer. Using refmap mixins.rift.refmap.json
at org.spongepowered.asm.mixin.transformer.MixinPreProcessorStandard.attachFields(MixinPreProcessorStandard.java:563) ~[mixin-0.7.11-SNAPSHOT.jar:0.7.11-SNAPSHOT+unknown-b0.git-unknown]
at org.spongepowered.asm.mixin.transformer.MixinPreProcessorStandard.attach(MixinPreProcessorStandard.java:263) ~[mixin-0.7.11-SNAPSHOT.jar:0.7.11-SNAPSHOT+unknown-b0.git-unknown]
at org.spongepowered.asm.mixin.transformer.MixinPreProcessorStandard.createContextFor(MixinPreProcessorStandard.java:241) ~[mixin-0.7.11-SNAPSHOT.jar:0.7.11-SNAPSHOT+unknown-b0.git-unknown]
at org.spongepowered.asm.mixin.transformer.MixinInfo.createContextFor(MixinInfo.java:1144) ~[mixin-0.7.11-SNAPSHOT.jar:0.7.11-SNAPSHOT+unknown-b0.git-unknown]
at org.spongepowered.asm.mixin.transformer.MixinApplicatorStandard.apply(MixinApplicatorStandard.java:268) ~[mixin-0.7.11-SNAPSHOT.jar:0.7.11-SNAPSHOT+unknown-b0.git-unknown]
at org.spongepowered.asm.mixin.transformer.TargetClassContext.applyMixins(TargetClassContext.java:353) ~[mixin-0.7.11-SNAPSHOT.jar:0.7.11-SNAPSHOT+unknown-b0.git-unknown]
at org.spongepowered.asm.mixin.transformer.MixinTransformer.apply(MixinTransformer.java:724) [mixin-0.7.11-SNAPSHOT.jar:0.7.11-SNAPSHOT+unknown-b0.git-unknown]
at org.spongepowered.asm.mixin.transformer.MixinTransformer.applyMixins(MixinTransformer.java:703) [mixin-0.7.11-SNAPSHOT.jar:0.7.11-SNAPSHOT+unknown-b0.git-unknown]
at org.spongepowered.asm.mixin.transformer.MixinTransformer.transformClassBytes(MixinTransformer.java:509) [mixin-0.7.11-SNAPSHOT.jar:0.7.11-SNAPSHOT+unknown-b0.git-unknown]
at org.spongepowered.asm.mixin.transformer.Proxy.transform(Proxy.java:72) [mixin-0.7.11-SNAPSHOT.jar:0.7.11-SNAPSHOT+unknown-b0.git-unknown]
at net.minecraft.launchwrapper.LaunchClassLoader.runTransformers(LaunchClassLoader.java:279) [launchwrapper-1.12.jar:?]
at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:176) [launchwrapper-1.12.jar:?]
at java.lang.ClassLoader.loadClass(Unknown Source) [?:1.8.0_291]
at java.lang.ClassLoader.loadClass(Unknown Source) [?:1.8.0_291]
at java.lang.Class.forName0(Native Method) ~[?:1.8.0_291]
at java.lang.Class.forName(Unknown Source) [?:1.8.0_291]
at net.minecraft.launchwrapper.Launch.launch(Launch.java:131) [launchwrapper-1.12.jar:?]
at net.minecraft.launchwrapper.Launch.main(Launch.java:28) [launchwrapper-1.12.jar:?]
at org.dimdev.riftloader.Main.main(Main.java:66) [Rift.jar:?]
[21:51:42] [main/ERROR]: Unable to launch
java.lang.ClassNotFoundException: net.minecraft.server.MinecraftServer
at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:191) ~[launchwrapper-1.12.jar:?]
at java.lang.ClassLoader.loadClass(Unknown Source) ~[?:1.8.0_291]
at java.lang.ClassLoader.loadClass(Unknown Source) ~[?:1.8.0_291]
at java.lang.Class.forName0(Native Method) ~[?:1.8.0_291]
at java.lang.Class.forName(Unknown Source) ~[?:1.8.0_291]
at net.minecraft.launchwrapper.Launch.launch(Launch.java:131) [launchwrapper-1.12.jar:?]
at net.minecraft.launchwrapper.Launch.main(Launch.java:28) [launchwrapper-1.12.jar:?]
at org.dimdev.riftloader.Main.main(Main.java:66) [Rift.jar:?]
Caused by: org.spongepowered.asm.mixin.transformer.throwables.MixinTransformerError: An unexpected critical error was encountered
at org.spongepowered.asm.mixin.transformer.MixinTransformer.transformClassBytes(MixinTransformer.java:521) ~[mixin-0.7.11-SNAPSHOT.jar:0.7.11-SNAPSHOT+unknown-b0.git-unknown]
at org.spongepowered.asm.mixin.transformer.Proxy.transform(Proxy.java:72) ~[mixin-0.7.11-SNAPSHOT.jar:0.7.11-SNAPSHOT+unknown-b0.git-unknown]
at net.minecraft.launchwrapper.LaunchClassLoader.runTransformers(LaunchClassLoader.java:279) ~[launchwrapper-1.12.jar:?]
at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:176) ~[launchwrapper-1.12.jar:?]
… 7 more
Caused by: org.spongepowered.asm.mixin.throwables.MixinApplyError: Mixin [mixins.rift.core.json:MixinMinecraftServer] from phase [DEFAULT] in config [mixins.rift.core.json] FAILED during APPLY
at org.spongepowered.asm.mixin.transformer.MixinTransformer.handleMixinError(MixinTransformer.java:779) ~[mixin-0.7.11-SNAPSHOT.jar:0.7.11-SNAPSHOT+unknown-b0.git-unknown]
at org.spongepowered.asm.mixin.transformer.MixinTransformer.handleMixinApplyError(MixinTransformer.java:732) ~[mixin-0.7.11-SNAPSHOT.jar:0.7.11-SNAPSHOT+unknown-b0.git-unknown]
at org.spongepowered.asm.mixin.transformer.MixinTransformer.transformClassBytes(MixinTransformer.java:513) ~[mixin-0.7.11-SNAPSHOT.jar:0.7.11-SNAPSHOT+unknown-b0.git-unknown]
at org.spongepowered.asm.mixin.transformer.Proxy.transform(Proxy.java:72) ~[mixin-0.7.11-SNAPSHOT.jar:0.7.11-SNAPSHOT+unknown-b0.git-unknown]
at net.minecraft.launchwrapper.LaunchClassLoader.runTransformers(LaunchClassLoader.java:279) ~[launchwrapper-1.12.jar:?]
at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:176) ~[launchwrapper-1.12.jar:?]
… 7 more
Caused by: org.spongepowered.asm.mixin.transformer.throwables.InvalidMixinException: Shadow field r was not located in the target class net.minecraft.server.MinecraftServer. Using refmap mixins.rift.refmap.json
at org.spongepowered.asm.mixin.transformer.MixinPreProcessorStandard.attachFields(MixinPreProcessorStandard.java:563) ~[mixin-0.7.11-SNAPSHOT.jar:0.7.11-SNAPSHOT+unknown-b0.git-unknown]
at org.spongepowered.asm.mixin.transformer.MixinPreProcessorStandard.attach(MixinPreProcessorStandard.java:263) ~[mixin-0.7.11-SNAPSHOT.jar:0.7.11-SNAPSHOT+unknown-b0.git-unknown]
at org.spongepowered.asm.mixin.transformer.MixinPreProcessorStandard.createContextFor(MixinPreProcessorStandard.java:241) ~[mixin-0.7.11-SNAPSHOT.jar:0.7.11-SNAPSHOT+unknown-b0.git-unknown]
at org.spongepowered.asm.mixin.transformer.MixinInfo.createContextFor(MixinInfo.java:1144) ~[mixin-0.7.11-SNAPSHOT.jar:0.7.11-SNAPSHOT+unknown-b0.git-unknown]
at org.spongepowered.asm.mixin.transformer.MixinApplicatorStandard.apply(MixinApplicatorStandard.java:268) ~[mixin-0.7.11-SNAPSHOT.jar:0.7.11-SNAPSHOT+unknown-b0.git-unknown]
at org.spongepowered.asm.mixin.transformer.TargetClassContext.applyMixins(TargetClassContext.java:353) ~[mixin-0.7.11-SNAPSHOT.jar:0.7.11-SNAPSHOT+unknown-b0.git-unknown]
at org.spongepowered.asm.mixin.transformer.MixinTransformer.apply(MixinTransformer.java:724) ~[mixin-0.7.11-SNAPSHOT.jar:0.7.11-SNAPSHOT+unknown-b0.git-unknown]
at org.spongepowered.asm.mixin.transformer.MixinTransformer.applyMixins(MixinTransformer.java:703) ~[mixin-0.7.11-SNAPSHOT.jar:0.7.11-SNAPSHOT+unknown-b0.git-unknown]
at org.spongepowered.asm.mixin.transformer.MixinTransformer.transformClassBytes(MixinTransformer.java:509) ~[mixin-0.7.11-SNAPSHOT.jar:0.7.11-SNAPSHOT+unknown-b0.git-unknown]
at org.spongepowered.asm.mixin.transformer.Proxy.transform(Proxy.java:72) ~[mixin-0.7.11-SNAPSHOT.jar:0.7.11-SNAPSHOT+unknown-b0.git-unknown]
at net.minecraft.launchwrapper.LaunchClassLoader.runTransformers(LaunchClassLoader.java:279) ~[launchwrapper-1.12.jar:?]
at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:176) ~[launchwrapper-1.12.jar:?]
… 7 more

Anything relating to mixins should be reported to the server softwares creators, not Sponge.

Mixins is a library that a lot of products use, and we do not support/manage those tools since we do not know them.