Fix crash when installed on a server

build.gradle

@@ -1,8 +1,7 @@
 buildscript {
 	repositories {
 		maven { url = 'https://files.minecraftforge.net/maven' }
-		maven { url = 'https://dist.creeper.host/Sponge/maven' }
-		jcenter()
+		maven { url = "https://repo.spongepowered.org/maven" }
 		mavenCentral()
 	}
 	
@@ -54,6 +53,19 @@ minecraft {
 				}
 			}
 		}
+		
+		server {
+			workingDirectory file('run')
+			
+			property 'mixin.env.disableRefMap', 'true'
+			arg '-mixin.config=bettercontrols.mixins.json'
+			
+			mods {
+				bettercontrols {
+					source sourceSets.main
+				}
+			}
+		}
 	}
 }
 

src/main/java/chylex/bettercontrols/BetterControlsMod.java

@@ -1,6 +1,10 @@
 package chylex.bettercontrols;
 import chylex.bettercontrols.config.BetterControlsConfig;
 import chylex.bettercontrols.gui.BetterControlsScreen;
+import net.minecraft.client.Minecraft;
+import net.minecraft.client.gui.screen.Screen;
+import net.minecraftforge.api.distmarker.Dist;
+import net.minecraftforge.fml.DistExecutor;
 import net.minecraftforge.fml.ExtensionPoint;
 import net.minecraftforge.fml.ModLoadingContext;
 import net.minecraftforge.fml.common.Mod;
@@ -10,10 +14,20 @@ import org.apache.commons.lang3.tuple.Pair;
 
 @Mod("bettercontrols")
 public final class BetterControlsMod{
-	public static final BetterControlsConfig config = BetterControlsConfig.load(FMLPaths.CONFIGDIR.get().resolve("BetterControls.json"));
+	public static final BetterControlsConfig config = DistExecutor.safeCallWhenOn(Dist.CLIENT, () -> ClientLoader::loadConfig);
 	
 	public BetterControlsMod(){
-		ModLoadingContext.get().registerExtensionPoint(ExtensionPoint.CONFIGGUIFACTORY, () -> (mc, parentScreen) -> new BetterControlsScreen(parentScreen));
+		ModLoadingContext.get().registerExtensionPoint(ExtensionPoint.CONFIGGUIFACTORY, () -> ClientLoader::createScreen);
 		ModLoadingContext.get().registerExtensionPoint(ExtensionPoint.DISPLAYTEST, () -> Pair.of(() -> FMLNetworkConstants.IGNORESERVERONLY, (a, b) -> true));
 	}
+	
+	private static final class ClientLoader {
+		public static BetterControlsConfig loadConfig() {
+			return BetterControlsConfig.load(FMLPaths.CONFIGDIR.get().resolve("BetterControls.json"));
+		}
+		
+		public static BetterControlsScreen createScreen(final Minecraft mc, final Screen parentScreen) {
+			return new BetterControlsScreen(parentScreen);
+		}
+	}
 }

src/main/resources/bettercontrols.mixins.json

@@ -3,7 +3,7 @@
   "minVersion": "0.8",
   "package": "chylex.bettercontrols.mixin",
   "compatibilityLevel": "JAVA_8",
-  "mixins": [
+  "client": [
     "AccessCameraFields",
     "AccessClientPlayerFields",
     "AccessControlsListCategory",