関連ワード:  java if string is null or empty    java check string is null or empty    java if string not null or empty    java 8 check if string is null or empty    java 17 check if string is null or empty    java 21 check if string is null or empty    java 11 check if string is null or empty    java check if string is null empty or whitespace    java if string is null return empty    java check string is not null or empty