Fix NPE when acceptableValues in defineInList() does not allow nulls, fixes #9300 (#9903)

src/main/java/net/minecraftforge/common/ForgeConfigSpec.java

@@ -330,7 +330,7 @@ public class ForgeConfigSpec extends UnmodifiableConfigWrapper<UnmodifiableConfi
             return defineInList(path, () -> defaultValue, acceptableValues);
         }
         public <T> ConfigValue<T> defineInList(List<String> path, Supplier<T> defaultSupplier, Collection<? extends T> acceptableValues) {
-            return define(path, defaultSupplier, acceptableValues::contains);
+            return define(path, defaultSupplier, o -> o != null && acceptableValues.contains(o));
         }
         //endregion