Remove unnecessary code in SecurityExpressionRoot

[lee-ext]

Code:

    private Set<String> getAuthoritySet() {
	if (roles == null) {
		roles = new HashSet<>();
		Collection<? extends GrantedAuthority> userAuthorities = authentication
				.getAuthorities();

		if (roleHierarchy != null) {
			userAuthorities = roleHierarchy
					.getReachableGrantedAuthorities(userAuthorities);
		}

		roles = AuthorityUtils.authorityListToSet(userAuthorities);
	}

	return roles;
}

The "roles = new HashSet<>();" is unnecessary and inefficiency.
Hope it can be modified.