関連ワード:  java test list is null or empty    java check if list is null or empty    java test if list is null or empty    java check if collection is null or empty    java 8 check if list is null or empty using optional    java check if list is not null or empty    java 17 check if list is null or empty    java util check if list is null or empty    java 8 check if list is null or empty    java 21 check if list is null or empty