Fix #4994 CoercionConfig for CoercionAction.AsNull not working on empty array deserialization

release-notes/VERSION-2.x

@@ -36,6 +36,9 @@ Project: jackson-databind
  (reported by @nlisker)
 #4932: Conversion of `MissingNode` throws `JsonProcessingException`
  (reported by @ludgerb)
+#4994: `CoercionConfig` for `CoercionAction.AsNull` not working on empty array deserialization
+ (reported by @Whi7y)
+ (fix by Joo-Hyuk K)
 
 2.18.2 (27-Nov-2024)
 

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

@@ -6,9 +6,8 @@
 import java.util.Objects;
 
 import com.fasterxml.jackson.annotation.JsonFormat;
-
-import com.fasterxml.jackson.core.*;
-
+import com.fasterxml.jackson.core.JsonParser;
+import com.fasterxml.jackson.core.JsonToken;
 import com.fasterxml.jackson.databind.*;
 import com.fasterxml.jackson.databind.annotation.JacksonStdImpl;
 import com.fasterxml.jackson.databind.cfg.CoercionAction;
@@ -237,6 +236,19 @@ public Object deserialize(JsonParser p, DeserializationContext ctxt)
             result = buffer.completeAndClearBuffer(chunk, ix, _elementClass);
         }
         ctxt.returnObjectBuffer(buffer);
+        // [databind#4949]: Coercion from empty array not applied
+        if (result.length == 0) {
+            result = coerceEmptyArray(result, ctxt);
+        }
+        return result;
+    }
+
+    private Object[] coerceEmptyArray(Object[] result, DeserializationContext ctxt)
+    {
+        final CoercionAction act = ctxt.findCoercionAction(logicalType(), handledType(), CoercionInputShape.EmptyArray);
+        if (act == CoercionAction.AsNull) {
+            return null;
+        }
         return result;
     }
 

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

@@ -179,6 +179,19 @@ public String[] deserialize(JsonParser p, DeserializationContext ctxt) throws IO
         }
         String[] result = buffer.completeAndClearBuffer(chunk, ix, String.class);
         ctxt.returnObjectBuffer(buffer);
+        // [databind#4949]: Coercion from empty array not applied
+        if (result.length == 0) {
+            result = coerceEmptyArray(result, ctxt);
+        }
+        return result;
+    }
+
+    private String[] coerceEmptyArray(String[] result, DeserializationContext ctxt)
+    {
+        final CoercionAction act = ctxt.findCoercionAction(logicalType(), handledType(), CoercionInputShape.EmptyArray);
+        if (act == CoercionAction.AsNull) {
+            return null;
+        }
         return result;
     }
 

src/test/java/com/fasterxml/jackson/databind/convert/CoerceEmptyArrayAsNull4994Test.java

@@ -0,0 +1,67 @@
+package com.fasterxml.jackson.databind.convert;
+
+import org.junit.jupiter.api.Test;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.cfg.CoercionAction;
+import com.fasterxml.jackson.databind.cfg.CoercionInputShape;
+import com.fasterxml.jackson.databind.testutil.DatabindTestUtil;
+
+import static org.junit.jupiter.api.Assertions.assertNull;
+
+// [databind#4994] CoercionConfig for empty arrays not working as expected
+public class CoerceEmptyArrayAsNull4994Test
+    extends DatabindTestUtil
+{
+    public static class StringArrayWrapper4994 {
+        public String[] value;
+    }
+
+    public static class ObjectArrayWrapper4994 {
+        public Object[] value;
+    }
+
+    public static class PojoArrayWrapper4994 {
+        public Pojo4994[] value;
+    }
+
+    public static class Pojo4994 {
+        public String name;
+        public int age;
+    }
+
+    private final String json = "{\"value\": []}";
+
+    private final ObjectMapper MAPPER_TO_NULL = jsonMapperBuilder()
+            .withCoercionConfigDefaults(cfg ->
+                    cfg.setCoercion(CoercionInputShape.EmptyArray, CoercionAction.AsNull))
+            .build();
+
+    @Test
+    public void testStringArrayAsNullCoercion()
+        throws Exception
+    {
+        StringArrayWrapper4994 pojo = MAPPER_TO_NULL.readValue(json, StringArrayWrapper4994.class);
+
+        assertNull(pojo.value); // expected: <null> but was: <[]>
+    }
+
+    @Test
+    public void testPojoArrayAsNullCoercion()
+            throws Exception
+    {
+        PojoArrayWrapper4994 wrapper = MAPPER_TO_NULL.readValue(json, PojoArrayWrapper4994.class);
+
+        assertNull(wrapper.value);
+    }
+
+    @Test
+    public void testObjectArrayAsNullCoercion()
+            throws Exception
+    {
+        ObjectArrayWrapper4994 wrapper = MAPPER_TO_NULL.readValue(json, ObjectArrayWrapper4994.class);
+
+        assertNull(wrapper.value);
+    }
+
+}