我正在尝试准备以下MySQL语句：
File -> Invalidate Caches/Restart
正在执行以下代码：
INSERT INTO Users (Username, Email, UserPassword) VALUES (?, ?, ?);但是$insertString = "INSERT INTO Users (Username, Email, UserPassword) VALUES (?, ?, ?);";
$statement = mysqli_prepare(
$insertString);
$statement->bind_param("sss",
$_POST["Username"], $_POST["Email"],
$_POST["UserPassword"]);
$statement->execute();
返回null。此代码有什么问题？