関連ワード:  java check for null or empty list    java list check if null or empty    java collection check if null or empty    java check if list is not null or empty    java check if list object is null or empty    java check null or empty collection    how to check if list is null or empty c#    java test if list is null or empty    how to check if list is null or empty    java 8 check if list is null or empty using optional