fix: getQuery() may have undefined values

[lomirus]

Hello, I am using Deno to try to write a chatroom demo, and now I think I've encountered a problem. Here's an example code:

const username = helpers.getQuery(context).username;

Here the VSCode just infers that the type of username is just string and wouldn't be undefined because the type of the return value of getQuery() is Record<string, string>. But in fact it sometimes does occur. And it also made me ignore considering the situation that the username would be empty so I didn't write the relevant code to check and avoid it. It may make debug hard so I just modified the type of the return value.

[CLAassistant]

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