fix: don't store duplicates in subtreePaths

Author: vera

src/main/java/edu/harvard/iq/dataverse/search/IndexServiceBean.java

@@ -2104,7 +2104,7 @@ private List<String> retrieveDVOPaths(DvObject dvo) {
         } catch (Exception ex) {
             logger.info("failed to find dataverseSegments for dataversePaths for " + SearchFields.SUBTREE + ": " + ex);
         }        
-        List<String> dataversePaths = getDataversePathsFromSegments(dataverseSegments);
+        Set<String> dataversePaths = new HashSet<>(getDataversePathsFromSegments(dataverseSegments));
         if (dataversePaths.size() > 0 && dvo.isInstanceofDataverse()) {
             // removing the dataverse's own id from the paths
             // fixes bug where if my parent dv was linked my dv was shown as linked to myself
@@ -2114,7 +2114,7 @@ private List<String> retrieveDVOPaths(DvObject dvo) {
         add linking paths
         */
         dataversePaths.addAll(findLinkingDataversePaths(findAllLinkingDataverses(dvo)));
-        return dataversePaths;
+        return new ArrayList<>(dataversePaths);
     }
 
     public String delete(Dataverse doomed) {