CategoryServiceImpl.add(): add check for empty string in addition to nullness.

Author: php-coder

src/main/java/ru/mystamps/web/service/CategoryServiceImpl.java

@@ -23,6 +23,7 @@
 import org.springframework.security.access.prepost.PreAuthorize;
 import org.springframework.transaction.annotation.Transactional;
 
+import org.apache.commons.lang3.StringUtils;
 import org.apache.commons.lang3.Validate;
 
 import org.slf4j.Logger;
@@ -60,7 +61,10 @@ public Category add(AddCategoryDto dto, User user) {
 		category.setNameRu(dto.getNameRu());
 
 		String slug = SlugUtils.slugify(dto.getName());
-		Validate.isTrue(slug != null, "Slug for string '%s' is null", dto.getName());
+		Validate.isTrue(
+			StringUtils.isNotEmpty(slug),
+			"Slug for string '%s' must be non empty", dto.getName()
+		);
 		category.setSlug(slug);
 
 		Date now = new Date();