fix : ObjectWriterAdapter#writeWithFilter support null input, for issue alibaba#1226

Author: wenshao

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

@@ -429,6 +429,11 @@ public boolean writeTypeInfo(JSONWriter jsonWriter) {
 
     @Override
     public void writeWithFilter(JSONWriter jsonWriter, Object object, Object fieldName, Type fieldType, long features) {
+        if (object == null) {
+            jsonWriter.writeNull();
+            return;
+        }
+
         if (jsonWriter.isWriteTypeInfo(object, fieldType, features)) {
             if (jsonWriter.jsonb) {
                 writeClassInfo(jsonWriter);

core/src/test/java/com/alibaba/fastjson2/issues_1000/Issue1226.java

@@ -0,0 +1,25 @@
+package com.alibaba.fastjson2.issues_1000;
+
+import com.alibaba.fastjson2.JSONFactory;
+import com.alibaba.fastjson2.JSONWriter;
+import com.alibaba.fastjson2.writer.ObjectWriterAdapter;
+import com.alibaba.fastjson2.writer.ObjectWriterProvider;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class Issue1226 {
+    @Test
+    public void test() {
+        ObjectWriterProvider provider = JSONFactory.getDefaultObjectWriterProvider();
+        ObjectWriterAdapter writerAdapter = (ObjectWriterAdapter) provider.getObjectWriter(Bean.class);
+
+        JSONWriter jsonWriter = JSONWriter.of();
+        writerAdapter.writeWithFilter(jsonWriter, null);
+        assertEquals("null", jsonWriter.toString());
+    }
+
+    static class Bean {
+        public int id;
+    }
+}