public DefaultSpaBuilder(IApplicationBuilder applicationBuilder, MulitSpaOptions options)
        {
            ApplicationBuilder = applicationBuilder
                                 ?? throw new ArgumentNullException(nameof(applicationBuilder));

            Options = options
                      ?? throw new ArgumentNullException(nameof(options));
        }
 /// <summary>
 /// Constructs a new instance of <see cref="MulitSpaOptions"/>.
 /// </summary>
 /// <param name="copyFromOptions">An instance of <see cref="MulitSpaOptions"/> from which values should be copied.</param>
 internal MulitSpaOptions(MulitSpaOptions copyFromOptions)
 {
     _defaultPage = copyFromOptions.DefaultPage;
     DefaultPageStaticFileOptions = copyFromOptions.DefaultPageStaticFileOptions;
     SourcePath = copyFromOptions.SourcePath;
 }