DiscordApiClient.PrepareMessage() throws NRE

Created by: ivan-ristovic

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Summary

NullReferenceException occurs when trying to upload a file with size greater than the allowed maximum.

Details

Stack trace:
   at DSharpPlus.Net.DiscordApiClient.PrepareMessage(JToken msg_raw)
   at DSharpPlus.Net.DiscordApiClient.UploadFileAsync(UInt64 channel_id, Stream file_data, String file_name, String content, Nullable`1 tts, DiscordEmbed embed)

The lib version is the latest nightly and the bot is running on .NET Core 2.1.

Steps to reproduce

1. Try to upload a large file (I tried >50MB one) via CommandContext.RespondWithFileAsync()
2. NRE

Notes

I have searched the code and I haven't found any checks on the Stream passed to DiscordApiClient.UploadFileAsync method. So I assume that the request returned contains null response string and that gets passed to DiscordApiClient.PrepareMessage() method, which then throws.