CustomCollections is now less invasive to ConversionService.

Removed the removal of the general collection-to-object converter as apparently some downstream Spring Data modules rely on it. This theoretically allows conversions of collections into maps but we now simply don't assume that not to work anymore.

Issue #2619.

Author: odrotbohm

src/main/java/org/springframework/data/util/CustomCollections.java

@@ -184,9 +184,6 @@ public static void registerConvertersIn(ConverterRegistry registry) {
 
 		Assert.notNull(registry, "ConverterRegistry must not be null!");
 
-		// Remove general collection to anything conversion as that would also convert collections to maps
-		registry.removeConvertible(Collection.class, Object.class);
-
 		REGISTRARS.forEach(it -> it.registerConvertersIn(registry));
 	}
 
@@ -352,6 +349,7 @@ public void registerConvertersIn(ConverterRegistry registry) {
 		 * @see org.springframework.data.util.CustomCollectionRegistrar#toJavaNativeCollection()
 		 */
 		@Override
+		@SuppressWarnings("null")
 		public Function<Object, Object> toJavaNativeCollection() {
 
 			return source -> source instanceof io.vavr.collection.Traversable

src/test/java/org/springframework/data/util/CustomCollectionsUnitTests.java

@@ -95,7 +95,6 @@ void conversListToVavr() {
 		assertThat(conversionService.canConvert(List.class, io.vavr.collection.Traversable.class)).isTrue();
 		assertThat(conversionService.canConvert(List.class, io.vavr.collection.List.class)).isTrue();
 		assertThat(conversionService.canConvert(List.class, io.vavr.collection.Set.class)).isTrue();
-		assertThat(conversionService.canConvert(List.class, io.vavr.collection.Map.class)).isFalse();
 
 		List<Integer> integers = Arrays.asList(1, 2, 3);
 
@@ -111,7 +110,6 @@ void convertsSetToVavr() {
 		assertThat(conversionService.canConvert(Set.class, io.vavr.collection.Traversable.class)).isTrue();
 		assertThat(conversionService.canConvert(Set.class, io.vavr.collection.Set.class)).isTrue();
 		assertThat(conversionService.canConvert(Set.class, io.vavr.collection.List.class)).isTrue();
-		assertThat(conversionService.canConvert(Set.class, io.vavr.collection.Map.class)).isFalse();
 
 		Set<Integer> integers = Collections.singleton(1);
 
@@ -143,7 +141,6 @@ void conversListToEclipse() {
 		assertThat(conversionService.canConvert(List.class, ImmutableList.class)).isTrue();
 		assertThat(conversionService.canConvert(List.class, ImmutableSet.class)).isTrue();
 		assertThat(conversionService.canConvert(List.class, ImmutableBag.class)).isTrue();
-		assertThat(conversionService.canConvert(List.class, ImmutableMap.class)).isFalse();
 
 		List<Integer> integers = Arrays.asList(1, 2, 3);
 
@@ -162,7 +159,6 @@ void convertsSetToEclipse() {
 		assertThat(conversionService.canConvert(Set.class, ImmutableSet.class)).isTrue();
 		assertThat(conversionService.canConvert(Set.class, ImmutableBag.class)).isTrue();
 		assertThat(conversionService.canConvert(Set.class, ImmutableList.class)).isTrue();
-		assertThat(conversionService.canConvert(Set.class, ImmutableMap.class)).isFalse();
 
 		Set<Integer> integers = Collections.singleton(1);