関連ワード:  java list is null or empty    java list is null or empty check    java list is not null or empty    java if list is null or empty    java 17 list is null or empty    java check if list is null or empty    java 8 check list is null or empty    java 17 check list is null or empty    java 8 check if list is null or empty using optional    java check list is not null or empty