code: public function visit(Criterion $criterion, CriterionVisitor $subVisitor = null)
      {
          $idSet = array();
          foreach ($criterion->value as $value) {
              foreach (explode('/', trim($value, '/')) as $id) {
                  $idSet[$id] = true;
              }
          }
  
          return '(' .
              implode(
                  ' OR ',
                  array_map(
                      function ($value) {
                          return 'location_id:"' . $value . '"';
                      },
                      array_keys($idSet)
                  )
              ) .
              ')';
      }
docs: Map field value to a proper Solr representation.
  
  @param \eZ\Publish\API\Repository\Values\Content\Query\Criterion $criterion
  @param \EzSystems\EzPlatformSolrSearchEngine\Query\CriterionVisitor $subVisitor
  
  @return string