fix : fill cache of InMemoryGroupDaoHandler with a Modifiable Map - E…

…XO-72017

Before this fix, when we call computeIfAbsent in
InMemoryGroupDaoHandler, and when the item is not in cache, then the
create map is done with Collections.emptyMap(). As this map is a non
modifiable map, it is not possible to create a group in a test after
that as it throws a UnsupportedExecption

This commit change the map to a classic empty Hashmap, so that it can be
updated in the future

Resolves Meeds-io/meeds#2068

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component/identity/src/test/java/org/exoplatform/services/organization/mock/InMemoryGroupHandler.java

@@ -175,7 +175,7 @@ public Group findGroupById(String groupId) {
 
   @Override
   public ListAccess<Group> findGroupChildren(Group parent, String keyword) {
-    List<Group> childGroups = groupChildsById.computeIfAbsent(parent.getId(), key -> Collections.emptyMap())
+    List<Group> childGroups = groupChildsById.computeIfAbsent(parent.getId(), key -> new HashMap<>())
                                              .values()
                                              .stream()
                                              .filter(group -> StringUtils.contains(group.getLabel(), keyword)
@@ -185,7 +185,7 @@ public ListAccess<Group> findGroupChildren(Group parent, String keyword) {
   }
 
   public Collection<Group> findGroups(Group parent) {
-    return groupChildsById.computeIfAbsent(parent.getId(), key -> Collections.emptyMap())
+    return groupChildsById.computeIfAbsent(parent.getId(), key -> new HashMap<>())
                           .values()
                           .stream()
                           .map(ObjectUtils::clone)