関連ワード:  java stream check if list is null or empty    java 8 check if list is null or empty using optional    java 8 check if list is null or empty    java 8 check if collection is null or empty    java 8 check if list is null or empty before stream    java list not null or empty    java check if list is null or empty  
結果 : java stream check if list is null or empty