fix: NPE when saving system configuration (#6417)

#### What type of PR is this?
/kind bug
/area core
/milestone 2.18.x

#### What this PR does / why we need it:
修复保存系统配置时出现的 NPE 问题

此问题由于 PR #6346 导致
#### Which issue(s) this PR fixes:
Fixes #6416

#### Does this PR introduce a user-facing change?
```release-note
None
```

application/src/main/java/run/halo/app/plugin/DefaultReactiveSettingFetcher.java

@@ -7,6 +7,7 @@ import com.fasterxml.jackson.databind.JsonNode;
 import com.fasterxml.jackson.databind.node.JsonNodeFactory;
 import java.util.LinkedHashMap;
 import java.util.Map;
+import java.util.Objects;
 import org.apache.commons.lang3.StringUtils;
 import org.springframework.beans.BeansException;
 import org.springframework.beans.factory.DisposableBean;
@@ -186,7 +187,7 @@ public class DefaultReactiveSettingFetcher
     @Override
     public Controller setupWith(ControllerBuilder builder) {
         ExtensionMatcher matcher =
-            extension -> configMapName.equals(extension.getMetadata().getName());
+            extension -> Objects.equals(extension.getMetadata().getName(), configMapName);
         return builder
             .extension(new ConfigMap())
             .syncAllOnStart(true)