[WO-97]: delete e-mail from user setting.

src/main/java/org/eclipse/openk/statementpublicaffairs/service/AdminService.java

@@ -263,7 +263,7 @@ public class AdminService {
 		if (settings == null) {
 			throw new BadRequestServiceException("Invalid settings format");
 		}
-		if (settings.getEmail() != null && !validEmailAddress(settings.getEmail())) {
+		if (settings.getEmail() != null && !settings.getEmail().isEmpty() && !validEmailAddress(settings.getEmail())) {
 			throw new BadRequestServiceException("Invalid email address format");
 		}