Fix #5203 (null handling for EnumSet deserializer) (#5382)

Author: cowtowncoder

release-notes/VERSION-2.x

@@ -10,6 +10,7 @@ Project: jackson-databind
 #5045: If there is a no-parameter constructor marked as `JsonCreator` and
   a constructor reported as `DefaultCreator`, latter is incorrectly used
  (reported by  @wrongwrong)
+#5203: Fix `null` handling of `EnumSetDeserializer`
 #5293: Fix minor typo in `PropertyBindingException.getMessageSuffix()`
  (reported by Johny L)
 #5313: Expose `getConverter()` in `StdDelegatingSerializer` for improved

src/main/java/com/fasterxml/jackson/databind/deser/std/EnumSetDeserializer.java

@@ -226,17 +226,26 @@ protected final EnumSet<?> _deserialize(JsonParser p, DeserializationContext ctx
                 // passed it to EnumDeserializer, too, but in general nulls should never be passed
                 // to non-container deserializers)
                 Enum<?> value;
-                if (t == JsonToken.VALUE_NULL) {
-                    if (_skipNullValues) {
+                if ((t == JsonToken.VALUE_NULL)
+                        // [databind#5203]: Custom deserializer may return null for non-null token
+                        || (value = _enumDeserializer.deserialize(p, ctxt)) == null) {
+                    value = (Enum<?>) _nullProvider.getNullValue(ctxt);
+                    if (value == null) {
+                        if (_skipNullValues) {
+                            continue;
+                        }
+                        // EnumSet does not accept nulls, so we need to report an error
+                        // 05-Nov-2025, tatu: In case of no explicit Nulls handling; with 2.x,
+                        //   let's just skip for backward compatibility; for 3.x, FAIL
+                        /*
+                        ctxt.handleUnexpectedToken(_enumType, JsonToken.VALUE_NULL, p,
+                                "`EnumSet` of type %s does not accept `null` values",
+                                ClassUtil.getTypeDescription(_enumType));
+                                */
                         continue;
                     }
-                    value = (Enum<?>) _nullProvider.getNullValue(ctxt);
-                } else {
-                    value = _enumDeserializer.deserialize(p, ctxt);
-                }
-                if (value != null) {
-                    result.add(value);
                 }
+                result.add(value);
             }
         } catch (Exception e) {
             throw JsonMappingException.wrapWithPath(e, result, result.size());

src/test/java/com/fasterxml/jackson/databind/tofix/EnumSetDeserializer5203Test.java renamed to src/test/java/com/fasterxml/jackson/databind/deser/enums/EnumSetDeserializer5203Test.java

@@ -1,9 +1,8 @@
-package com.fasterxml.jackson.databind.tofix;
+package com.fasterxml.jackson.databind.deser.enums;
 
 import java.io.IOException;
 import java.util.EnumSet;
 
-import com.fasterxml.jackson.databind.testutil.failure.JacksonTestFailureExpected;
 import org.junit.jupiter.api.Test;
 
 import com.fasterxml.jackson.annotation.JsonSetter;
@@ -16,14 +15,16 @@
 import com.fasterxml.jackson.databind.exc.InvalidNullException;
 import com.fasterxml.jackson.databind.json.JsonMapper;
 import com.fasterxml.jackson.databind.module.SimpleModule;
+import com.fasterxml.jackson.databind.testutil.DatabindTestUtil;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertThrows;
-import static org.junit.jupiter.api.Assertions.assertTrue;
 
 // For [databind#5203]
 public class EnumSetDeserializer5203Test
+    extends DatabindTestUtil
 {
-    public enum MyEnum {
+    enum MyEnum {
         FOO
     }
 
@@ -57,40 +58,45 @@ public MyEnum deserialize(JsonParser p, DeserializationContext ctxt) throws IOEx
         }
     }
 
-    private ObjectMapper createMapperWithCustomDeserializer() {
-        SimpleModule module = new SimpleModule();
-        module.addDeserializer(MyEnum.class, new EmptyStringToNullDeserializer());
-
-        return JsonMapper.builder()
-                .addModule(module)
-                .defaultSetterInfo(JsonSetter.Value.forContentNulls(Nulls.FAIL))
-                .build();
+    @Test
+    public void nullsDefaultTest() throws Exception {
+        // In 2.x, default is to skip nulls (for backwards-compatibility)
+        final ObjectMapper mapper = createMapperWithCustomDeserializer(Nulls.DEFAULT);
+        _verifySkipResult(mapper);
     }
 
-    @JacksonTestFailureExpected
     @Test
-    public void nullsFailTest() {
-        ObjectMapper mapper = createMapperWithCustomDeserializer();
+    public void nullsFailTest() throws Exception {
+        final ObjectMapper mapper = createMapperWithCustomDeserializer(Nulls.FAIL);
 
         assertThrows(
                 InvalidNullException.class,
                 () -> mapper.readValue("{\"set\":[\"\"]}", new TypeReference<Dst>(){})
         );
     }
-
-    @JacksonTestFailureExpected
+    
     @Test
     public void nullsSkipTest() throws Exception {
+        final ObjectMapper mapper = createMapperWithCustomDeserializer(Nulls.SKIP);
+        _verifySkipResult(mapper);
+    }
+
+    private ObjectMapper createMapperWithCustomDeserializer(Nulls nullHandling) {
         SimpleModule module = new SimpleModule();
         module.addDeserializer(MyEnum.class, new EmptyStringToNullDeserializer());
 
-        ObjectMapper mapper = JsonMapper.builder()
+        return JsonMapper.builder()
                 .addModule(module)
-                .defaultSetterInfo(JsonSetter.Value.forContentNulls(Nulls.SKIP))
+                .defaultSetterInfo(JsonSetter.Value.forContentNulls(nullHandling))
                 .build();
+    }
 
+    private void _verifySkipResult(ObjectMapper mapper) throws Exception
+    {
         Dst dst = mapper.readValue("{\"set\":[\"FOO\",\"\"]}", new TypeReference<Dst>() {});
 
-        assertTrue(dst.getSet().isEmpty(), "Null values should be skipped");
+        // Null value (from empty string) should be skipped, but FOO should be present
+        assertEquals(1, dst.getSet().size());
+        assertEquals(MyEnum.FOO, dst.getSet().iterator().next());
     }
 }

src/test/java/com/fasterxml/jackson/databind/deser/jdk/EnumMapDeserializer5165Test.java

@@ -10,9 +10,7 @@
 import com.fasterxml.jackson.databind.ObjectMapper;
 import com.fasterxml.jackson.databind.exc.InvalidNullException;
 import com.fasterxml.jackson.databind.json.JsonMapper;
-import org.opentest4j.AssertionFailedError;
 
-import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 import static org.junit.jupiter.api.Assertions.assertThrows;