Simplify ServerRequestExtensions.queryParamOrNull()

[esperar]

What this PR is about is

Null value processing has been modified more concisely.

---

While I was looking at the implementation of ServerRequestExtensions on the webflux side of the spring framework, I think I can correct it more correlatedly by putting the default string "" in the function named queryParamOrNull() when the parameter value is null.

And instead of the CollectionUtil library, I used isNullOrEmpty() provided by the Kotlin standard library.

I've tried handling null values using the elvis operator, please check it out and merge this PR if you like it!

---

Before

fun ServerRequest.queryParamOrNull(name: String): String? {
	val queryParamValues = queryParams()[name]
	return if (CollectionUtils.isEmpty(queryParamValues)) {
		null
	} else {
		var value: String? = queryParamValues!![0]
		if (value == null) {
			value = ""
		}
		value
	}
}

After

fun ServerRequest.queryParamOrNull(name: String): String? {
	val queryParamValues = queryParams()[name]
	return if (queryParamValues.isNullOrEmpty()) null else queryParamValues[0] ?: ""
}

Thank you :)

[sbrannen]

Hi @esperar,

Please do not "request a review" from individual team members using the GitHub feature.

Somebody in the team will get to it as soon as their schedule permits.

Thanks

[esperar]

I apologize. I thought it was omitted because there was no comment after the test comment.