The share-by-map BDAY-to-ICS conversion builds a placeholder mapping for
the SUMMARY/DESCRIPTION/alarm templates. Each block sets the fallback
marker for its own placeholder (e.g. {nickname} -> '!nickname!', {n:f} ->
'!n:f!'), but the {fn} block wrote the empty-FN fallback to {nickname}
instead of {fn}.
As a result, for a VCARD whose FN is present but empty, a genuine
NICKNAME was overwritten with '!fn!' in the generated event, and the
{fn} placeholder never received its '!fn!' marker, so a '[{fn}|...]'
fallback in a template failed to resolve.
Assign the fallback to {fn}, matching the surrounding blocks.
Co-Authored-By: Claude <noreply@anthropic.com>
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