diff --git a/adminer/drivers/mssql.inc.php b/adminer/drivers/mssql.inc.php
index 77bfc83c..29852871 100644
--- a/adminer/drivers/mssql.inc.php
+++ b/adminer/drivers/mssql.inc.php
@@ -26,7 +26,7 @@ if (isset($_GET["mssql"])) {
 				$this->error = rtrim($this->error);
 			}
 
-			function attach(?string $server, string $username, string $password): string {
+			function attach(string $server, string $username, string $password): string {
 				$connection_info = array("UID" => $username, "PWD" => $password, "CharacterSet" => "UTF-8");
 				$ssl = adminer()->connectSsl();
 				if (isset($ssl["Encrypt"])) {
@@ -182,7 +182,7 @@ if (isset($_GET["mssql"])) {
 			class Db extends MssqlDb {
 				public $extension = "PDO_SQLSRV";
 
-				function attach(?string $server, string $username, string $password): string {
+				function attach(string $server, string $username, string $password): string {
 					list($host, $port) = host_port($server);
 					return $this->dsn("sqlsrv:Server=$host" . ($port ? ",$port" : ""), $username, $password);
 				}
@@ -192,7 +192,7 @@ if (isset($_GET["mssql"])) {
 			class Db extends MssqlDb {
 				public $extension = "PDO_DBLIB";
 
-				function attach(?string $server, string $username, string $password): string {
+				function attach(string $server, string $username, string $password): string {
 					list($host, $port) = host_port($server);
 					return $this->dsn("dblib:charset=utf8;host=$host" . ($port ? (is_numeric($port) ? ";port=" : ";unix_socket=") . $port : ""), $username, $password);
 				}
@@ -217,7 +217,7 @@ if (isset($_GET["mssql"])) {
 		public $generated = array("PERSISTED", "VIRTUAL");
 		public $onActions = "NO ACTION|CASCADE|SET NULL|SET DEFAULT";
 
-		static function connect(?string $server, string $username, string $password) {
+		static function connect(string $server, string $username, string $password) {
 			if ($server == "") {
 				$server = "localhost:1433";
 			}
diff --git a/adminer/drivers/mysql.inc.php b/adminer/drivers/mysql.inc.php
index 8ba4e68b..b731772b 100644
--- a/adminer/drivers/mysql.inc.php
+++ b/adminer/drivers/mysql.inc.php
@@ -16,7 +16,7 @@ if (!defined('Adminer\DRIVER')) {
 				parent::init();
 			}
 
-			function attach(?string $server, string $username, string $password): string {
+			function attach(string $server, string $username, string $password): string {
 				mysqli_report(MYSQLI_REPORT_OFF); // stays between requests, not required since PHP 5.3.4
 				list($host, $port) = host_port($server);
 				$ssl = adminer()->connectSsl();
@@ -58,14 +58,14 @@ if (!defined('Adminer\DRIVER')) {
 		class Db extends SqlDb {
 			/** @var resource */ private $link;
 
-			function attach(?string $server, string $username, string $password): string {
+			function attach(string $server, string $username, string $password): string {
 				if (ini_bool("mysql.allow_local_infile")) {
 					return lang('Disable %s or enable %s or %s extensions.', "'mysql.allow_local_infile'", "MySQLi", "PDO_MySQL");
 				}
 				$this->link = @mysql_connect(
 					($server != "" ? $server : ini_get("mysql.default_host")),
-					("$server$username" != "" ? $username : ini_get("mysql.default_user")),
-					("$server$username$password" != "" ? $password : ini_get("mysql.default_password")),
+					($server . $username != "" ? $username : ini_get("mysql.default_user")),
+					($server . $username . $password != "" ? $password : ini_get("mysql.default_password")),
 					true,
 					131072 // CLIENT_MULTI_RESULTS for CALL
 				);
@@ -158,7 +158,7 @@ if (!defined('Adminer\DRIVER')) {
 		class Db extends PdoDb {
 			public $extension = "PDO_MySQL";
 
-			function attach(?string $server, string $username, string $password): string {
+			function attach(string $server, string $username, string $password): string {
 				$options = array(\PDO::MYSQL_ATTR_LOCAL_INFILE => false);
 				$ssl = adminer()->connectSsl();
 				if ($ssl) {
@@ -212,7 +212,7 @@ if (!defined('Adminer\DRIVER')) {
 		public $functions = array("char_length", "date", "from_unixtime", "lower", "round", "floor", "ceil", "sec_to_time", "time_to_sec", "upper");
 		public $grouping = array("avg", "count", "count distinct", "group_concat", "max", "min", "sum");
 
-		static function connect(?string $server, string $username, string $password) {
+		static function connect(string $server, string $username, string $password) {
 			$connection = parent::connect($server, $username, $password);
 			if (is_string($connection)) {
 				if (function_exists('iconv') && !is_utf8($connection) && strlen($s = iconv("windows-1250", "utf-8", $connection)) > strlen($connection)) { // windows-1250 - most common Windows encoding
diff --git a/adminer/drivers/oracle.inc.php b/adminer/drivers/oracle.inc.php
index 90b53069..69bf941b 100644
--- a/adminer/drivers/oracle.inc.php
+++ b/adminer/drivers/oracle.inc.php
@@ -20,7 +20,7 @@ if (isset($_GET["oracle"])) {
 				$this->error = $error;
 			}
 
-			function attach(?string $server, string $username, string $password): string {
+			function attach(string $server, string $username, string $password): string {
 				$this->link = @oci_new_connect($username, $password, $server, "AL32UTF8");
 				if ($this->link) {
 					$this->server_info = oci_server_version($this->link);
@@ -110,7 +110,7 @@ if (isset($_GET["oracle"])) {
 			public $extension = "PDO_OCI";
 			public $_current_db;
 
-			function attach(?string $server, string $username, string $password): string {
+			function attach(string $server, string $username, string $password): string {
 				return $this->dsn("oci:dbname=//$server;charset=AL32UTF8", $username, $password);
 			}
 
diff --git a/adminer/drivers/pgsql.inc.php b/adminer/drivers/pgsql.inc.php
index 73827af3..f2ceb625 100644
--- a/adminer/drivers/pgsql.inc.php
+++ b/adminer/drivers/pgsql.inc.php
@@ -20,7 +20,7 @@ if (isset($_GET["pgsql"])) {
 				$this->error = $error;
 			}
 
-			function attach(?string $server, string $username, string $password): string {
+			function attach(string $server, string $username, string $password): string {
 				$db = adminer()->database();
 				set_error_handler(array($this, '_error'));
 				list($host, $port) = host_port(addcslashes($server, "'\\"));
@@ -144,7 +144,7 @@ if (isset($_GET["pgsql"])) {
 			public $extension = "PDO_PgSQL";
 			public $timeout = 0;
 
-			function attach(?string $server, string $username, string $password): string {
+			function attach(string $server, string $username, string $password): string {
 				$db = adminer()->database();
 				list($host, $port) = host_port(addcslashes($server, "'\\"));
 				//! client_encoding is supported since 9.1, but we can't yet use min_version here
@@ -212,7 +212,7 @@ if (isset($_GET["pgsql"])) {
 
 		public string $nsOid = "(SELECT oid FROM pg_namespace WHERE nspname = current_schema())";
 
-		static function connect(?string $server, string $username, string $password) {
+		static function connect(string $server, string $username, string $password) {
 			$connection = parent::connect($server, $username, $password);
 			if (is_string($connection)) {
 				return $connection;
diff --git a/adminer/drivers/sqlite.inc.php b/adminer/drivers/sqlite.inc.php
index c1608eb7..a11ef6fc 100644
--- a/adminer/drivers/sqlite.inc.php
+++ b/adminer/drivers/sqlite.inc.php
@@ -11,7 +11,7 @@ if (isset($_GET["sqlite"])) {
 			public $extension = "SQLite3";
 			private $link;
 
-			function attach(?string $filename, string $username, string $password): string {
+			function attach(string $filename, string $username, string $password): string {
 				$this->link = new \SQLite3($filename);
 				$version = $this->link->version();
 				$this->server_info = $version["versionString"];
@@ -75,7 +75,7 @@ if (isset($_GET["sqlite"])) {
 		abstract class SqliteDb extends PdoDb {
 			public $extension = "PDO_SQLite";
 
-			function attach(?string $filename, string $username, string $password): string {
+			function attach(string $filename, string $username, string $password): string {
 				$this->dsn(DRIVER . ":$filename", "", "");
 				$this->query("PRAGMA foreign_keys = 1");
 				$this->query("PRAGMA busy_timeout = 500");
@@ -87,7 +87,7 @@ if (isset($_GET["sqlite"])) {
 
 	if (class_exists('Adminer\SqliteDb')) {
 		class Db extends SqliteDb {
-			function attach(?string $filename, string $username, string $password): string {
+			function attach(string $filename, string $username, string $password): string {
 				parent::attach($filename, $username, $password);
 				$this->query("PRAGMA foreign_keys = 1");
 				$this->query("PRAGMA busy_timeout = 500");
@@ -122,7 +122,7 @@ if (isset($_GET["sqlite"])) {
 		public $functions = array("hex", "length", "lower", "round", "unixepoch", "upper");
 		public $grouping = array("avg", "count", "count distinct", "group_concat", "max", "min", "sum");
 
-		static function connect(?string $server, string $username, string $password) {
+		static function connect(string $server, string $username, string $password) {
 			if ($password != "") {
 				return lang('Database does not support password.');
 			}
diff --git a/adminer/include/bootstrap.inc.php b/adminer/include/bootstrap.inc.php
index f4701d31..f2bbc0fa 100644
--- a/adminer/include/bootstrap.inc.php
+++ b/adminer/include/bootstrap.inc.php
@@ -91,7 +91,7 @@ Adminer::$instance =
 include "../adminer/drivers/mysql.inc.php"; // must be included as last driver
 
 define('Adminer\JUSH', Driver::$jush);
-define('Adminer\SERVER', $_GET[DRIVER]); // read from pgsql=localhost, '' means default server, null means no server
+define('Adminer\SERVER', "" . $_GET[DRIVER]); // read from pgsql=localhost, '' means default server
 define('Adminer\DB', "$_GET[db]"); // for the sake of speed and size
 define(
 	'Adminer\ME',
diff --git a/adminer/include/db.inc.php b/adminer/include/db.inc.php
index 549987b3..18a9fd07 100644
--- a/adminer/include/db.inc.php
+++ b/adminer/include/db.inc.php
@@ -18,7 +18,7 @@ abstract class SqlDb {
 	/** Connect to server
 	* @return string error message
 	*/
-	abstract function attach(?string $server, string $username, string $password): string;
+	abstract function attach(string $server, string $username, string $password): string;
 
 	/** Quote string to use in SQL
 	* @return string escaped string enclosed in '
diff --git a/adminer/include/driver.inc.php b/adminer/include/driver.inc.php
index 713fd420..eb7f656f 100644
--- a/adminer/include/driver.inc.php
+++ b/adminer/include/driver.inc.php
@@ -34,7 +34,7 @@ abstract class SqlDriver {
 	/** Connect to the database
 	* @return Db|string string for error
 	*/
-	static function connect(?string $server, string $username, string $password) {
+	static function connect(string $server, string $username, string $password) {
 		$connection = new Db;
 		return ($connection->attach($server, $username, $password) ?: $connection);
 	}