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