Bean Validation API의 NotNull, NotEmpty, NotBlank의 차이에 대해 설명한다. @NotNull The annotated element must not be null. Accepts any type. 모든 타입에 대해 null을 허용하지 않는다. @NotEmpty The annotated element must not be null nor empty. Supported types are: CharSequence (length of character sequence is evaluated) Collection (collection size is evaluated) Map (map size is evaluated) Array (array length is evaluated) ..