Null normalizes to 'f' when PDO::ATTR_EMULATE_PREPARES = true

Description

The following code:

<?php

$pdo = new PDO(
    'pgsql:host=localhost;port=5432;dbname=test',
    'postgres',
    'postgres',
    [
        PDO::ATTR_EMULATE_PREPARES => true,
    ],
);

/** @var PDOStatement $stmt */
$stmt = $pdo->prepare('SELECT :bool_val as bv');
$stmt->bindValue(':bool_val', null, PDO::PARAM_BOOL);
$stmt->execute();

foreach ($stmt->getIterator() as $item) {
    var_dump($item['bv']);
}

Resulted in this output:

string(1) "f"

But I expected this output instead:

NULL

When ATTR_EMULATE_PREPARES not used, NULL is actually returned.

PHP Version

PHP 8.2.11

Operating System

Alpine Linux 3.18

在启用和禁用 PDO::ATTR_EMULATE_PREPARES 的情况下，使用 PostgreSQL 重现所提供的 PDO 示例，重点关注使用 PDO::PARAM_BOOL 和 null 值的 bindValue()。跟踪 PDO 的模拟 prepare 路径并比较两种结果；当模拟 prepare 也返回 NULL，且该行为由回归测试覆盖时即完成。