diff --git a/Elwig/Services/MemberService.cs b/Elwig/Services/MemberService.cs
index 424b36b..1acdf9d 100644
--- a/Elwig/Services/MemberService.cs
+++ b/Elwig/Services/MemberService.cs
@@ -549,7 +549,7 @@ namespace Elwig.Services {
 
             ctx.RemoveRange(ctx.MemberTelephoneNrs.Where(t => t.MgNr == oldMgNr));
             ctx.AddRange(vm.PhoneNrs
-                .Where(input => input.Number != null)
+                .Where(input => input.Number != null && input.Number != "")
                 .Select((input, i) => new MemberTelNr {
                     MgNr = m.MgNr,
                     Nr = i + 1,
diff --git a/Elwig/Windows/AdministrationWindow.cs b/Elwig/Windows/AdministrationWindow.cs
index 96aaa8f..d4f96a3 100644
--- a/Elwig/Windows/AdministrationWindow.cs
+++ b/Elwig/Windows/AdministrationWindow.cs
@@ -402,7 +402,7 @@ namespace Elwig.Windows {
 
         protected bool InputLostFocus(TextBox input, ValidationResult res, string? msg = null) {
             if (DoShowWarningWindows && !res.IsValid && !IsClosing && (IsEditing || IsCreating))
-                MessageBox.Show(res.ErrorContent.ToString(), msg ?? res.ErrorContent.ToString(), MessageBoxButton.OK, MessageBoxImage.Warning);
+                MessageBox.Show(res.ErrorContent?.ToString(), msg ?? res.ErrorContent?.ToString(), MessageBoxButton.OK, MessageBoxImage.Warning);
             return res.IsValid;
         }