Revert workaround for Java 8 `ConcurrentHashMap` bug.

Closes #3060

src/main/java/org/springframework/data/convert/CustomConversions.java

@@ -536,11 +536,7 @@ public class CustomConversions {
 		public Class<?> computeIfAbsent(Class<?> sourceType, Class<?> targetType,
 				Function<ConvertiblePair, Class<?>> mappingFunction) {
 
-			TargetTypes targetTypes = customReadTargetTypes.get(sourceType);
-
-			if (targetTypes == null) {
-				targetTypes = customReadTargetTypes.computeIfAbsent(sourceType, TargetTypes::new);
-			}
+			TargetTypes targetTypes = customReadTargetTypes.computeIfAbsent(sourceType, TargetTypes::new);
 
 			return targetTypes.computeIfAbsent(targetType, mappingFunction);
 		}

src/main/java/org/springframework/data/convert/DefaultTypeMapper.java

@@ -124,14 +124,7 @@ public class DefaultTypeMapper<S> implements TypeMapper<S>, BeanClassLoaderAware
 	 */
 	@Nullable
 	private TypeInformation<?> getFromCacheOrCreate(Alias alias) {
-
-		Optional<TypeInformation<?>> typeInformation = typeCache.get(alias);
-
-		if (typeInformation == null) {
-			typeInformation = typeCache.computeIfAbsent(alias, getAlias);
-		}
-
-		return typeInformation.orElse(null);
+		return typeCache.computeIfAbsent(alias, getAlias).orElse(null);
 	}
 
 	@Override