Spring Simplify ServerRequestExtensions.queryParamOrNull()

What this PR is about is

Null value processing has been modified more concisely.

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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!

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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 :)

Comment From: 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

Comment From: esperar

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