public String toString() {
        return getPrincipals() != null ? getPrincipals().toString() : "empty";
    }
Returns {@link #getPrincipals() principals}.toString() if they are not null, otherwise prints out the string
&quot;empty&quot;

@return the String representation of this Account object.
core/src/main/java/org/apache/shiro/authc/SimpleAccount.java