The email address is not requires in this case, the template assumes it exists. Wrap the content in a guard like other templates do.
<tal:email tal:condition"context/owner/preferredemail"> ... </tal:email>
The email address is not requires in this case, the template assumes it exists. Wrap the content in a guard like other templates do.
<tal:email tal:condition" context/ owner/preferred email">
...
</tal:email>