public AuthenticationInfo beforeAllAttempts(Collection<? extends Realm> realms, AuthenticationToken token)
            throws AuthenticationException {
        return null;
    }
Returns {@code null} immediately, relying on this class's {@link #merge merge} implementation to return
only the first {@code info} object it encounters, ignoring all subsequent ones.
core/src/main/java/org/apache/shiro/authc/pam/FirstSuccessfulStrategy.java