in commons-email2-jakarta/src/main/java/org/apache/commons/mail2/jakarta/MultiPartEmail.java [453:466]
public Email setMsg(final String msg) throws EmailException {
EmailException.checkNonEmpty(msg, () -> "Invalid message.");
try {
final BodyPart primary = getPrimaryBodyPart();
if (primary instanceof MimePart && EmailUtils.isNotEmpty(getCharsetName())) {
((MimePart) primary).setText(msg, getCharsetName());
} else {
primary.setText(msg);
}
} catch (final MessagingException e) {
throw new EmailException(e);
}
return this;
}