fix serialize List<String> error, for issue #1826

core/src/main/java/com/alibaba/fastjson2/JSONWriterJSONB.java

@@ -669,6 +669,7 @@ public void writeString(List<String> list) {
                 String str = list.get(i);
                 if (str == null) {
                     writeNull();
+                    continue;
                 }
                 int coder = STRING_CODER.applyAsInt(str);
                 if (coder != LATIN) {

core/src/test/java/com/alibaba/fastjson2/issues_1800/Issue1826.java

@@ -0,0 +1,28 @@
+package com.alibaba.fastjson2.issues_1800;
+
+import com.alibaba.fastjson2.JSONB;
+import org.junit.jupiter.api.Test;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class Issue1826 {
+    @Test
+    public void test() {
+        Bean bean = new Bean();
+        bean.values = new ArrayList<>();
+        bean.values.add("a");
+        bean.values.add(null);
+        bean.values.add("b");
+
+        byte[] bytes = JSONB.toBytes(bean);
+        Bean bean1 = JSONB.parseObject(bytes, Bean.class);
+        assertEquals(bean.values, bean1.values);
+    }
+
+    public static class Bean {
+        public List<String> values;
+    }
+}

test-jdk17/src/test/java/com/alibaba/fastjson2/fastcode/BigDecimalTest.java

@@ -0,0 +1,30 @@
+package com.alibaba.fastjson2.fastcode;
+
+import org.junit.jupiter.api.Test;
+import sun.misc.Unsafe;
+
+import java.lang.reflect.Field;
+import java.lang.reflect.Method;
+import java.math.BigDecimal;
+
+public class BigDecimalTest {
+    @Test
+    public void test() throws Throwable {
+        Field theUnsafeField = Unsafe.class.getDeclaredField("theUnsafe");
+        theUnsafeField.setAccessible(true);
+        Unsafe unsafe = (Unsafe) theUnsafeField.get(null);
+        Method objectFieldOffset = Unsafe.class.getMethod("objectFieldOffset", Field.class);
+        long stringCacheOffset = (Long) objectFieldOffset.invoke(
+                unsafe,
+                BigDecimal.class.getDeclaredField("stringCache")
+        );
+
+        BigDecimal d = BigDecimal.valueOf(12345, 2);
+        unsafe.putObject(d, stringCacheOffset, null);
+
+        d.toString();
+        System.out.println(unsafe.getObject(d, stringCacheOffset));
+        unsafe.putObject(d, stringCacheOffset, null);
+        System.out.println(unsafe.getObject(d, stringCacheOffset));
+    }
+}