fix compile error for issue #1440

core/src/main/java/com/alibaba/fastjson2/writer/ObjectWriterImplCollection.java

@@ -159,14 +159,12 @@ public void write(JSONWriter jsonWriter, Object object, Object fieldName, Type f
                 i++;
                 continue;
             }
-            
+
             Class<?> itemClass = item.getClass();
             ObjectWriter itemObjectWriter;
             if (itemClass == previousClass) {
                 itemObjectWriter = previousObjectWriter;
             } else {
-                Class<?> itemClass = item.getClass();
-                ObjectWriter itemObjectWriter;
                 if (itemClass == previousClass) {
                     itemObjectWriter = previousObjectWriter;
                 } else {

core/src/test/java/com/alibaba/fastjson2/writer/ObjectWriterSetTest.java

@@ -1,23 +1,20 @@
 package com.alibaba.fastjson2.writer;
 
-import static org.junit.jupiter.api.Assertions.assertEquals;
+import com.alibaba.fastjson2.JSON;
+import org.junit.jupiter.api.Test;
 
 import java.util.HashSet;
 import java.util.Set;
 
-import org.junit.jupiter.api.Test;
-
-import com.alibaba.fastjson2.JSON;
+import static org.junit.jupiter.api.Assertions.assertEquals;
 
 public class ObjectWriterSetTest {
-
     @Test
     public void testJsonbSet() {
         Set<Integer> set = new HashSet<Integer>();
         set.add(1);
         set.add(null);
         String str = JSON.toJSONString(set);
-
         assertEquals(str, "[null,1]");
     }
 }