Updated the protected Storage constructor in Storage.cs to coalesce t…

…he supplied logger value to NullLoggerFactory.Instance, so that if a caller constructs an instance of BackblazeClient using the default logger value (which is null) then it still works.

src/Client/Client/Storage/Storage.cs

@@ -28,6 +28,8 @@ protected Storage(HttpClient client, IClientOptions options, ILoggerFactory logg
             try
             {
                 // Initialize components
+                logger ??= NullLoggerFactory.Instance;
+
                 _client = new ApiClient(client, options, logger.CreateLogger<ApiClient>(), cache);
                 _logger = logger.CreateLogger<Storage>();
             }