diff --git a/e-invoicing-domain/src/main/kotlin/net/codinux/invoicing/mail/MailReader.kt b/e-invoicing-domain/src/main/kotlin/net/codinux/invoicing/mail/MailReader.kt
index 66d5d41..8f44d55 100644
--- a/e-invoicing-domain/src/main/kotlin/net/codinux/invoicing/mail/MailReader.kt
+++ b/e-invoicing-domain/src/main/kotlin/net/codinux/invoicing/mail/MailReader.kt
@@ -110,7 +110,7 @@ class MailReader(
 
             if (attachmentsWithEInvoice.isNotEmpty()) {
                 return MailWithInvoice(
-                    message.from?.joinToString(), message.subject,
+                    message.from?.joinToString(), message.subject ?: "",
                     message.sentDate?.let { map(it) }, map(message.receivedDate), message.messageNumber,
                     getPlainTextBody(parts), getHtmlBody(parts),
                     attachmentsWithEInvoice