Store#birthday_of was the last nil-returning read with a row && in
lib; it now reads the one row with sole and rescues NoMatchingRow at
the method, #contact's shape. #delete_group keeps its first-and-return
read and now gives its own reason rather than borrowing this one's.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013VNdx5qiRSWADBoVfDRcrd

diff --git a/lib/pro_tacts/store.rb b/lib/pro_tacts/store.rb
index 09cbcc1..ddd11ac 100644
--- a/lib/pro_tacts/store.rb
+++ b/lib/pro_tacts/store.rb
@@ -789,11 +789,11 @@ module ProTacts
     # #delete's shape.
     #: (String id) -> bool
     def delete_group(id)
-      # A plain `first` read, #birthday_of's reason: id is the primary
-      # key, so there is no ambiguity for `sole` to catch. Read here
-      # rather than rescued around the whole method, which would have
-      # swallowed a NoMatchingRow raised from inside the transaction
-      # below and answered it as an ordinary miss.
+      # A plain `first` read rather than #group's rescued `sole`: a
+      # rescue around the whole method would swallow a NoMatchingRow
+      # raised from inside the transaction below and answer it as an
+      # ordinary miss. id is the primary key, so there is no ambiguity
+      # for `sole` to catch.
       row = groups.where(id:).first
       return false if row.nil?
 
@@ -1204,13 +1204,13 @@ module ProTacts
       }
     end
 
-    # One card's birthday, or nil for none. A plain `first` read rather
-    # than `sole`: card_id is the primary key, so there is no ambiguity
-    # for `sole` to catch and no row is the ordinary answer.
+    # One card's birthday, or nil for none — the ordinary answer, a
+    # birthday being optional, so it is rescued here, #contact's shape.
     #: (String id) -> Birthday?
     def birthday_of(id)
-      row = birthdays.where(card_id: id).first
-      row && birthday_from(row)
+      birthday_from(birthdays.where(card_id: id).sole)
+    rescue Sequel::NoMatchingRow
+      nil
     end
 
     # The content lines a contact inherits, each beside the group