Fix NPE when acceptableValues in defineInList() does not allow nulls, backport of #9903 (#9907)

Co-authored-by: J-RAP <SrRapero720@hotmail.com>

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

@@ -346,7 +346,7 @@ 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));
         }
         public <T> ConfigValue<List<? extends T>> defineList(String path, List<? extends T> defaultValue, Predicate<Object> elementValidator) {
             return defineList(split(path), defaultValue, elementValidator);