feat: add setter method to define custom NullValueSerializer

Author: AnneMayor

src/main/java/org/springframework/data/redis/serializer/GenericJackson2JsonRedisSerializer.java

@@ -21,6 +21,7 @@
 import java.util.function.Consumer;
 import java.util.function.Supplier;
 
+import com.fasterxml.jackson.databind.JsonSerializer;
 import org.springframework.cache.support.NullValue;
 import org.springframework.core.KotlinDetector;
 import org.springframework.data.util.Lazy;
@@ -231,6 +232,10 @@ public static void registerNullValueSerializer(ObjectMapper objectMapper, @Nulla
 		objectMapper.registerModule(new SimpleModule().addSerializer(new NullValueSerializer(classPropertyTypeName)));
 	}
 
+	public void registerCustomNullValueSerializer(JsonSerializer<?> nullValueSerializer) {
+		this.mapper.registerModule(new SimpleModule().addSerializer(nullValueSerializer));
+	}
+
 	/**
 	 * Gets the configured {@link ObjectMapper} used internally by this {@link GenericJackson2JsonRedisSerializer} to
 	 * de/serialize {@link Object objects} as {@literal JSON}.

src/test/java/org/springframework/data/redis/serializer/GenericJackson2JsonRedisSerializerUnitTests.java

@@ -40,6 +40,9 @@
 import java.util.concurrent.atomic.AtomicReference;
 import java.util.function.Consumer;
 
+import com.fasterxml.jackson.core.JsonGenerator;
+import com.fasterxml.jackson.databind.SerializerProvider;
+import com.fasterxml.jackson.databind.ser.std.StdSerializer;
 import org.junit.jupiter.api.Test;
 import org.mockito.Mockito;
 
@@ -420,7 +423,7 @@ void deserializesJavaTimeFrimBytes() {
 	}
 
 	@Test // GH-2601
-	public void internalObjectMapperCustomization() {
+	void internalObjectMapperCustomization() {
 
 		GenericJackson2JsonRedisSerializer serializer = new GenericJackson2JsonRedisSerializer();
 
@@ -438,14 +441,34 @@ public void internalObjectMapperCustomization() {
 	}
 
 	@Test // GH-2601
-	public void configureWithNullConsumerThrowsIllegalArgumentException() {
+	void configureWithNullConsumerThrowsIllegalArgumentException() {
 
 		assertThatIllegalArgumentException()
 			.isThrownBy(() -> new GenericJackson2JsonRedisSerializer().configure(null))
 			.withMessage("Consumer used to configure and customize ObjectMapper must not be null")
 			.withNoCause();
 	}
 
+	@Test
+	void customSerializeAndDeserializeNullValue() {
+
+		GenericJackson2JsonRedisSerializer serializer = new GenericJackson2JsonRedisSerializer();
+		String expected = "null";
+
+		serializer.registerCustomNullValueSerializer(new StdSerializer<>(String.class) {
+			@Override
+			public void serialize(String value, JsonGenerator gen, SerializerProvider provider) throws IOException {
+				gen.writeRawValue(expected);
+			}
+		});
+
+		byte[] serializedValue = serializer.serialize(expected);
+		assertThat(serializedValue).isNotNull();
+
+		Object deserializedValue = serializer.deserialize(serializedValue);
+		assertThat(deserializedValue).isNull();
+	}
+
 	private static void serializeAndDeserializeNullValue(GenericJackson2JsonRedisSerializer serializer) {
 
 		NullValue nv = BeanUtils.instantiateClass(NullValue.class);