diff --git a/models/print.model b/models/print.model
index 9bb1cd8d1..201256662 100644
--- a/models/print.model
+++ b/models/print.model
@@ -5,7 +5,7 @@ PrintJob
   created       UTCTime
   acknowledged  UTCTime Maybe
   recipient     UserId Maybe          OnDeleteCascade OnUpdateCascade   -- optional as some letters may contain just an address
-  sender        UserId Maybe                                            -- senders and associations are optional
+  sender        UserId Maybe          OnDeleteSetNull OnUpdateCascade   -- senders and associations are optional
   course        CourseId Maybe        OnDeleteCascade OnUpdateCascade
   qualification QualificationId Maybe OnDeleteCascade OnUpdateCascade
   lmsUser       LmsUserId       Maybe OnDeleteCascade OnUpdateCascade   -- allows tracking if recipient has been notified
diff --git a/src/Jobs/Handler/SendNotification/Qualification.hs b/src/Jobs/Handler/SendNotification/Qualification.hs
index c4491cdf7..07051aaa3 100644
--- a/src/Jobs/Handler/SendNotification/Qualification.hs
+++ b/src/Jobs/Handler/SendNotification/Qualification.hs
@@ -67,7 +67,7 @@ dispatchNotificationQualificationRenewal nQualification jRecipient = do
       lmsIdent  = lmsUserIdent & getLmsIdent
       lmsUrl    = "https://drive.fraport.de"
       lmsLogin  = lmsUrl <> "/?login=" <> lmsIdent
-      prepAddress upa = userDisplayName : (upa & html2textlines) -- TODO: use supervisor's address 
+      prepAddress upa = userDisplayName : (upa & html2textlines) -- TODO: use supervisor's address, once implemented
       pdfMeta   = mkMeta
                   [ toMeta "date"           letterDate
                   , toMeta "lang"          (selectDeEn userLanguages)    -- select either German or English only, see Utils.Lang