diff --git a/BeWoPlanerMobil/Util/JsonCustomer.cs b/BeWoPlanerMobil/Util/JsonCustomer.cs
index ac91fce04..ca38afcaa 100644
--- a/BeWoPlanerMobil/Util/JsonCustomer.cs
+++ b/BeWoPlanerMobil/Util/JsonCustomer.cs
@@ -82,7 +82,10 @@ namespace BeWoPlanerMobil.Util
 
             Kommentar = init.Notice;
 
-            init.CostBearers?.DoForEach(cb => { ReferenceNumbers.AddIfNotIn(new ReferenceNumberWithNotice(cb.ReferenceNumber, cb.Notice, cb.CostBearer.Name)); });
+            init.CostBearers?.Where(costBearer => !string.IsNullOrWhiteSpace(costBearer.ReferenceNumber)).DoForEach(cb =>
+            {
+                ReferenceNumbers.AddIfNotIn(new ReferenceNumberWithNotice(cb.ReferenceNumber, cb.Notice, cb.CostBearer.Name));
+            });
 
             foreach(var iContactDC in init.ContactInformations)
             {