Fix: slash command options parsing

[samarmeena]

Issue

1. create a slash command with two optional options, example: /test option_a option_b
2. now on discord use this command as /test option_b: 123 (here we are using option_b only and leaving option_a blank)
3. when discord.ts try to execute the original command, parameter passed are [123, undefined] (which is the issue, because it was suppose to [undefined, 123])

Fix

I have looked at the code, I think, this suggested approach is more appropriate.

Thanks

[samarmeena]

this pull messed up xd