refactor(CollectionController): simplify a check for emptiness.

Author: php-coder

src/main/java/ru/mystamps/web/feature/collection/CollectionController.java

@@ -70,7 +70,7 @@ public String showInfoBySlug(
 			collectionService.findSeriesInCollection(collectionId, lang);
 		model.addAttribute("seriesOfCollection", seriesOfCollection);
 
-		if (seriesOfCollection.iterator().hasNext()) {
+		if (!seriesOfCollection.isEmpty()) {
 			long categoryCounter = categoryService.countCategoriesOf(collectionId);
 			long countryCounter  = countryService.countCountriesOf(collectionId);
 			long seriesCounter   = collectionService.countSeriesOf(collectionId);