code: public Set<String> getVersions( String groupId, String artifactId )
      {
          Set<String> result = new TreeSet<String>();
          for ( int i = 0; i < stores.length; i++ )
          {
              Set<String> versions = stores[i].getVersions( groupId, artifactId );
              if ( versions != null )
              {
                  result.addAll( versions );
              }
          }
          return result;
      }
docs: {@inheritDoc}