title: Discord.NET: Bot not processing input
body: <p>I'm trying to make a "warning" command for a bot which takes a SocketGuildUser parameter, adds 1 to a warning int. However, when I try to enter a user @mention for SocketGuildUser, which should work, an exception is thrown.</p>
  
  <pre><code>[Command("warn")]
      public async Task WarnUser(SocketGuildUser user)
      {
          string warningDirectory = @"D:\HumbleBot\HumbleBot\Warnings";
          string warningText = @"D:\HumbleBot\HumbleBot\Warnings\warnings.json";
  
          if (!Directory.Exists(warningDirectory))
              Directory.CreateDirectory(warningDirectory);
  
          Dictionary&lt;ulong, uint&gt; UserWarnings = new Dictionary&lt;ulong, uint&gt;();
          UserWarnings = JsonConvert.DeserializeObject
                         &lt;Dictionary&lt;ulong, uint&gt;&gt;
                         (File.ReadAllText(warningText));
  
          if (!UserWarnings.ContainsKey(id)) //Exception thrown here
              UserWarnings.Add(id, 0);
  
          UserWarnings.TryGetValue(id, out uint warningNum);
          UserWarnings[id] = warningNum++;
  
          string json = JsonConvert.SerializeObject(UserWarnings);
          File.WriteAllText(warningText, json);
          //builder
      }
  </code></pre>
  
  <p>Input: ~warn @Stratus#6727
  Output (in Console): Object reference not set to an instance of an object.</p>
  
  <p>EDIT: Added the rest of the code; as it turns out it has something to do with that and not what I'd added. It probably has something to do with the file reading/writing, or I'm using JsonConvert the wrong way.</p>