Null check wasn't picking up the slack when InformationVersion is not found.

src/Discord.Net/DiscordConfig.cs

@@ -5,7 +5,7 @@ namespace Discord
     public class DiscordConfig
     {
         public const int APIVersion = 6;        
-        public static string Version { get; } = typeof(DiscordRestConfig).GetTypeInfo().Assembly?.GetCustomAttribute<AssemblyInformationalVersionAttribute>().InformationalVersion ?? "Unknown";
+        public static string Version { get; } = typeof(DiscordRestConfig).GetTypeInfo().Assembly?.GetCustomAttribute<AssemblyInformationalVersionAttribute>()?.InformationalVersion ?? "Unknown";
 
         public static readonly string ClientAPIUrl = $"https://discordapp.com/api/v{APIVersion}/";
         public const string CDNUrl = "https://cdn.discordapp.com/";