#28059 Refactor HostVariableAPIImpl to use ImmutableList

The HostVariableAPIImpl was refactored to make use of Google's Immutable List implementation for returned site variables in the getUniqueSiteVariables() method. We previously used an ArrayList, but have made the shift for its immutable properties and thread-safety.

dotCMS/src/main/java/com/dotmarketing/portlets/hostvariable/bussiness/HostVariableAPIImpl.java

@@ -11,6 +11,7 @@
 import com.dotmarketing.exception.DotSecurityException;
 import com.dotmarketing.portlets.contentlet.business.HostAPI;
 import com.dotmarketing.portlets.hostvariable.model.HostVariable;
+import com.google.common.collect.ImmutableList;
 import com.liferay.portal.language.LanguageException;
 import com.liferay.portal.model.User;
 import java.util.ArrayList;
@@ -166,9 +167,9 @@ public List<HostVariable> save(final List<HostVariable> siteVariables, final Str
 	 * @param siteVariables The list of site variables.
 	 * @return A new ArrayList containing only the unique site variables based on their keys.
 	 */
-	private ArrayList<HostVariable> getUniqueSiteVariables(List<HostVariable> siteVariables) {
+	private List<HostVariable> getUniqueSiteVariables(List<HostVariable> siteVariables) {
 
-		return new ArrayList<>(siteVariables.stream().
+		return ImmutableList.copyOf(siteVariables.stream().
 				collect(Collectors.toMap(
 						HostVariable::getKey, // key is the HostVariable's `key`
 						hostVariable -> hostVariable,  // value is the HostVariable itself