message property
The text of a violation instead of defaultMessage; null keeps the
default.
{min}-style placeholders take the constraint's attributes,
${validatedValue} the invalid value, and {some.key} a message of
the validator's validationMessageSource. This text is the violation
message and the field error's default message; a messages.properties
key such as NotBlank.signup.name still wins when errors are shown
through a message source.
Implementation
final String? message;