null check.
null check.

krororo/review,kuad9/review_study,kmuto/review,takahashim/review,murashitas/review,kuad9/review_study,orangain/review,masawada/review,takahashim/review,krororo/review,suzuki/review,krororo/review,kmuto/review,kmuto/review,suzuki/review,orangain/review,murashitas/review,masawada/review