no data exception and no documentation warnings in generated code

DbService.cs

@@ -12,9 +12,10 @@ namespace de.hottis.genericdatabaseapiservice.Services {
         Task<List<TOUT>> ReadBySelect<TIN, TOUT>(string selectStatement, TIN input);
     } 
 
+    public class DbServiceException : Exception {}
+    public class NotDataFoundException : DbServiceException {}
+
     public class DbService : IDbService {
-
-
         async public Task<List<TOUT>> ReadBySelect<TIN, TOUT>(string selectStatement, TIN input) {
             var itemList = new List<TOUT>();
 
@@ -57,6 +58,11 @@ namespace de.hottis.genericdatabaseapiservice.Services {
                     } 
                 } 
             } 
+
+            if (itemList.Count == 0) {
+                throw new NotDataFoundException();
+            }
+
             return itemList;
         } 
     }