Regression fix for #4741 Include.NON_DEFAULT setting used on POJO, empty values are not included in json if default is null

release-notes/VERSION-2.x

@@ -6,6 +6,10 @@ Project: jackson-databind
 
 2.18.1 (WIP-2024)
 
+#4741: When `Include.NON_DEFAULT` setting is used on POJO, empty values
+  are not included in json if default is `null`
+ (reported by @ragnhov)
+ (fix by Joo-Hyuk K)
 #4749: Fixed a problem with `StdDelegatingSerializer#serializeWithType` looking up the serializer
   with the wrong argument
  (fix by wrongwrong)

src/main/java/com/fasterxml/jackson/databind/ser/PropertyBuilder.java

@@ -182,8 +182,12 @@ protected BeanPropertyWriter buildWriter(SerializerProvider prov,
             }
             if (valueToSuppress == null) {
                 suppressNulls = true;
-                // [databind#4464] NON_DEFAULT does not work with NON_EMPTY for custom serializer
-                valueToSuppress = BeanPropertyWriter.MARKER_FOR_EMPTY;
+                // [databind#4471] Different behavior when Include.NON_DEFAULT
+                //   setting is used on POJO vs global setting, as per documentation.
+                if (!_useRealPropertyDefaults) {
+                    // [databind#4464] NON_DEFAULT does not work with NON_EMPTY for custom serializer
+                    valueToSuppress = BeanPropertyWriter.MARKER_FOR_EMPTY;
+                }
             } else {
                 if (valueToSuppress.getClass().isArray()) {
                     valueToSuppress = ArrayBuilders.getArrayComparator(valueToSuppress);

src/test/java/com/fasterxml/jackson/databind/ser/filter/JsonInclude4741Test.java

@@ -0,0 +1,34 @@
+package com.fasterxml.jackson.databind.ser.filter;
+
+import org.junit.jupiter.api.Test;
+
+import com.fasterxml.jackson.annotation.JsonInclude;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.testutil.DatabindTestUtil;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class JsonInclude4741Test
+    extends DatabindTestUtil
+{
+    @JsonInclude(JsonInclude.Include.NON_DEFAULT)
+    public static class MyString {
+        public String value = null;
+    }
+
+    private final ObjectMapper MAPPER = newJsonMapper();
+
+    @Test
+    void testSerialization() throws Exception
+    {
+        MyString input = new MyString();
+        input.value = "";
+
+        String json = MAPPER.writeValueAsString(input);
+        assertEquals(a2q("{'value':''}"), json);
+
+        MyString output = MAPPER.readValue(json, MyString.class);
+
+        assertEquals(input.value, output.value);
+    }
+}