I can't get into my own server! Please help!

I can't get into my own server that I was building! All I did was use a command that I copied and pasted into the chat to get a custom firework!

As soon as I pressed enter I was immediately sent to the "Server list" page.

When I try to rejoin it comes up with the bug report:

Internal Exception:io.netty.handler.codec.DecoderException:java.lang.IndexOutOfBoundsException: readerIndex(93) + length(1) exceeds writerIndex(93): PooledUnsafeDirectByteBuf(ridx: 93, widx: 93, cap: 93)

If anyone could help that would be great!!