GH-2298 - Read empty collections as empty values

Author: won-seoop

src/main/java/org/springframework/data/redis/core/convert/MappingRedisConverter.java

@@ -101,6 +101,7 @@
  * @author Mark Paluch
  * @author Golam Mazid Sajib
  * @author Leehyoungwoo
+ * @author Hyeonseop Won
  * @since 1.7
  */
 public class MappingRedisConverter implements RedisConverter, InitializingBean {
@@ -852,7 +853,7 @@ private void writeToBucket(String path, @Nullable Object value, RedisData sink,
 			}
 		}
 
-		return isArray ? toArray(target, collectionType, valueType) : (target.isEmpty() ? null : target);
+		return isArray ? toArray(target, collectionType, valueType) : target;
 	}
 
 	/**

src/test/java/org/springframework/data/redis/core/convert/ConversionTestEntities.java

@@ -45,6 +45,7 @@
  * @author Mark Paluch
  * @author Golam Mazid Sajib
  * @author John Blum
+ * @author Hyeonseop Won
  */
 public class ConversionTestEntities {
 
@@ -61,6 +62,7 @@ public static class Person {
 		Gender gender;
 
 		List<String> nicknames;
+		Set<String> aliases;
 		List<Person> coworkers;
 		List<Integer> positions;
 		Integer age;

src/test/java/org/springframework/data/redis/core/convert/MappingRedisConverterUnitTests.java

@@ -64,6 +64,7 @@
  * @author Mark Paluch
  * @author Golam Mazid Sajib
  * @author John Blum
+ * @author Hyeonseop Won
  */
 @ExtendWith(MockitoExtension.class)
 class MappingRedisConverterUnitTests {
@@ -286,6 +287,22 @@ void readConvertsListOfSimplePropertiesCorrectly() {
 		assertThat(converter.read(Person.class, rdo).nicknames).containsExactly("dragon reborn", "lews therin");
 	}
 
+	@Test // GH-2298
+	void readConvertsEmptyListToEmptyCollection() {
+
+		RedisData rdo = new RedisData(Bucket.newBucketFromStringMap(Collections.emptyMap()));
+
+		assertThat(converter.read(Person.class, rdo).nicknames).isEmpty();
+	}
+
+	@Test // GH-2298
+	void readConvertsEmptySetToEmptyCollection() {
+
+		RedisData rdo = new RedisData(Bucket.newBucketFromStringMap(Collections.emptyMap()));
+
+		assertThat(converter.read(Person.class, rdo).aliases).isEmpty();
+	}
+
 	@Test // DATAREDIS-425
 	void readConvertsUnorderedListOfSimplePropertiesCorrectly() {
 
@@ -1880,7 +1897,7 @@ void readInnerListShouldNotInfluenceOuterWithSameNameWhenNull() {
 
 		Outer outer = read(Outer.class, source);
 
-		assertThat(outer.values).isNull();
+		assertThat(outer.values).isEmpty();
 		assertThat(outer.inners.get(0).values).isEqualTo(Arrays.asList("i-1", "i-2"));
 	}