Optimize codes

Author: steverao

instrumentation/apache-dubbo-2.7/library-autoconfigure/src/main/java/io/opentelemetry/instrumentation/apachedubbo/v2_7/DubboHeadersGetter.java

@@ -7,6 +7,7 @@
 
 import io.opentelemetry.context.propagation.TextMapGetter;
 import java.lang.reflect.Method;
+import java.util.Collections;
 import java.util.Map;
 import org.apache.dubbo.rpc.RpcInvocation;
 
@@ -17,17 +18,19 @@ enum DubboHeadersGetter implements TextMapGetter<DubboRequest> {
   @SuppressWarnings("unchecked") // unchecked for 2.7.6, 2.7.7
   public Iterable<String> keys(DubboRequest request) {
     RpcInvocation invocation = request.invocation();
-    // In 2.7.6, 2.7.7, the StringToObjectMap implementation does not correctly retrieve the keySet,
-    // so always call getObjectAttachments when it is present.
     try {
+      // In 2.7.6, 2.7.7, the StringToObjectMap implementation does not correctly retrieve the keySet.
+      // Therefore, it's advisable to always call getObjectAttachments when it is available.
       Method getObjectAttachmentsMethod = invocation.getClass().getMethod("getObjectAttachments");
       if (getObjectAttachmentsMethod != null) {
         return ((Map<String, Object>) getObjectAttachmentsMethod.invoke(invocation)).keySet();
+      } else {
+        return invocation.getAttachments().keySet();
       }
     } catch (Exception e) {
       // ignore
     }
-    return invocation.getAttachments().keySet();
+    return Collections.emptyList();
   }
 
   @Override