public void addStringPermissions(Collection<String> permissions) {
        if (this.stringPermissions == null) {
            this.stringPermissions = new HashSet<String>();
        }
        this.stringPermissions.addAll(permissions);
    }
Adds (assigns) multiple permissions to those associated directly with the account.  If the account doesn't yet
have any string-based permissions, a  new permissions collection (a Set&lt;String&gt;) will be created automatically.

@param permissions the permissions to add to those associated directly with the account.
core/src/main/java/org/apache/shiro/authz/SimpleAuthorizationInfo.java