public FilterBuilder(FileFilterCollection fileFilterCollection, params string[] extensions)
            {
                if (fileFilterCollection == null) throw new ArgumentNullException("FileFilterCollection may not be null");
                if (!extensions.Any() || extensions.All(String.IsNullOrWhiteSpace)) throw new ArgumentException("you must specify at least one extension");

                FileFilterCollection = fileFilterCollection;
                Extensions = extensions;
            }
            public FilterBuilder(FileFilterCollection fileFilterCollection, params string[] extensions)
            {
                if (fileFilterCollection == null)
                {
                    throw new ArgumentNullException("FileFilterCollection may not be null");
                }
                if (!extensions.Any() || extensions.All(String.IsNullOrWhiteSpace))
                {
                    throw new ArgumentException("you must specify at least one extension");
                }

                FileFilterCollection = fileFilterCollection;
                Extensions           = extensions;
            }