According to RFC 5321 and 5322, mailboxes at top level domain names are permitted. Thus, the syntax localpart@tld is valid. Explicit text to this topic can be found in RFC 5321:
2.3.5. Domain Names
A domain name (or often just a "domain") consists of one or more
components, separated by dots if more than one appears. In the case
of a top-level domain used by itself in an email address, a single
string is used without any dots.
Accordingly, the code
EmailValidator ev = EmailValidator.getInstance();
should output "true".