if query parameter value processing is different when value is empty or null

Description

The following code:

CASE 1:

<?php
$url = "http://localhost:8964/?soap";
CASE1:
parse_url($url);
echo var_dump(parse_url($url));
$query = parse_str(parse_url($url)["query"], $result);
echo var_dump($result);
$http_query  = http_build_query($result);
echo $http_query;

//CASE2 assign query param value to null 

$result["soap"]=null;
echo $http_query;

//CASE 3 - replicate same as case 2 but in other form  and results are different.
$arr = array('test' => null);

echo http_build_query($arr);

?>

array(5) {
  ["scheme"]=>
  string(4) "http"
  ["host"]=>
  string(9) "localhost"
  ["port"]=>
  int(8964)
  ["path"]=>
  string(1) "/"
  ["query"]=>
  string(4) "soap"
}
array(1) {
  ["soap"]=>
  string(0) ""
}
soap=soap=

But I expected this output instead:
CASE1: soap=
CASE2: soap
CASE3 soap

PS: if query param value is empty string or null , but query param should be in url.

PHP Version

PHP 8.1.2

Operating System

No response

Reproduce the three cases using parse_url(), parse_str(), and http_build_query() with the sample URL and arrays. Read the existing tests for these functions and compare handling of missing, empty-string, and null values. Done means the intended query representation is documented by tests and the observed outputs are consistent with that behavior.