定休日を未入力で登録した場合のシステムエラーを修正

[nanasess]

Fixes #828

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 50.60%. Comparing base (03fa814) to head (4a1a061).
Report is 5 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1108   +/-   ##
=======================================
  Coverage   50.60%   50.60%           
=======================================
  Files          80       80           
  Lines       10258    10258           
=======================================
  Hits         5191     5191           
  Misses       5067     5067           

Flag	Coverage Δ
tests	50.60% <ø> (ø)

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