refactor: fix nullable params

src/main/java/emu/grasscutter/game/achievement/Achievements.java

@@ -231,6 +231,10 @@ public class Achievements {
                             });
 
             var a = this.getAchievement(i);
+            if(a == null) {
+                Grasscutter.getLogger().warn("null returned while getting achievement!");
+                return;
+            }
             a.setStatus(Status.STATUS_REWARD_TAKEN);
             this.save();
             this.sendUpdatePacket(a);

src/main/java/emu/grasscutter/game/activity/condition/AllActivityConditionBuilder.java

@@ -25,7 +25,7 @@ public class AllActivityConditionBuilder {
     private Map<ActivityConditions, ActivityConditionBaseHandler> initActivityConditions() {
         Reflections reflector = Grasscutter.reflector;
         return reflector.getTypesAnnotatedWith(ActivityCondition.class).stream()
-                .map(this::newInstance)
+            .map(this::newInstance).filter(Objects::nonNull)
                 .map(h -> new AbstractMap.SimpleEntry<>(extractActionType(h), h))
                 .collect(
                         Collectors.toMap(AbstractMap.SimpleEntry::getKey, AbstractMap.SimpleEntry::getValue));

src/main/java/emu/grasscutter/utils/lang/Language.java

@@ -347,7 +347,7 @@ public final class Language {
                                                 return Files.getLastModifiedTime(path).toMillis();
                                             } catch (Exception ignored) {
                                                 Grasscutter.getLogger()
-                                                        .debug("Exception while checking modified time: ", path);
+                                                        .debug("Exception while checking modified time: {}", path);
                                                 return Long.MAX_VALUE; // Don't use cache, something has gone wrong
                                             }
                                         })