diff --git a/src/Monolog/Handler/AmqpHandler.php b/src/Monolog/Handler/AmqpHandler.php
index ba45dd51..33fffccd 100644
--- a/src/Monolog/Handler/AmqpHandler.php
+++ b/src/Monolog/Handler/AmqpHandler.php
@@ -32,14 +32,14 @@ class AmqpHandler extends AbstractProcessingHandler
 
     /**
      * @param AMQPExchange|AMQPChannel $exchange     AMQPExchange (php AMQP ext) or PHP AMQP lib channel, ready for use
-     * @param string                   $exchangeName Optional exchange name, for AMQPChannel (PhpAmqpLib) only
+     * @param string|null              $exchangeName Optional exchange name, for AMQPChannel (PhpAmqpLib) only
      * @param string|int               $level        The minimum logging level at which this handler will be triggered
      * @param bool                     $bubble       Whether the messages that are handled can bubble up the stack or not
      */
     public function __construct($exchange, ?string $exchangeName = null, $level = Logger::DEBUG, bool $bubble = true)
     {
         if ($exchange instanceof AMQPChannel) {
-            $this->exchangeName = $exchangeName;
+            $this->exchangeName = (string) $exchangeName;
         } elseif (!$exchange instanceof AMQPExchange) {
             throw new \InvalidArgumentException('PhpAmqpLib\Channel\AMQPChannel or AMQPExchange instance required');
         } elseif ($exchangeName) {
diff --git a/src/Monolog/Handler/BrowserConsoleHandler.php b/src/Monolog/Handler/BrowserConsoleHandler.php
index 620e2e67..7ff2b160 100755
--- a/src/Monolog/Handler/BrowserConsoleHandler.php
+++ b/src/Monolog/Handler/BrowserConsoleHandler.php
@@ -74,7 +74,7 @@ class BrowserConsoleHandler extends AbstractProcessingHandler
         }
     }
 
-    public function close()
+    public function close(): void
     {
         self::resetStatic();
     }
diff --git a/src/Monolog/Handler/GroupHandler.php b/src/Monolog/Handler/GroupHandler.php
index 28b9f162..309d3be9 100644
--- a/src/Monolog/Handler/GroupHandler.php
+++ b/src/Monolog/Handler/GroupHandler.php
@@ -102,7 +102,7 @@ class GroupHandler extends Handler implements ProcessableHandlerInterface, Reset
         }
     }
 
-    public function close()
+    public function close(): void
     {
         parent::close();
 
diff --git a/src/Monolog/Logger.php b/src/Monolog/Logger.php
index 1c05293c..79b7d836 100644
--- a/src/Monolog/Logger.php
+++ b/src/Monolog/Logger.php
@@ -135,7 +135,7 @@ class Logger implements LoggerInterface, ResettableInterface
     protected $timezone;
 
     /**
-     * @var ?callable
+     * @var callable|null
      */
     protected $exceptionHandler;
 
@@ -343,7 +343,7 @@ class Logger implements LoggerInterface, ResettableInterface
      * This is useful at the end of a request and will be called automatically on every handler
      * when they get destructed.
      */
-    public function close()
+    public function close(): void
     {
         foreach ($this->handlers as $handler) {
             $handler->close();
@@ -360,7 +360,7 @@ class Logger implements LoggerInterface, ResettableInterface
      * have a long running process like a worker or an application server serving multiple requests
      * in one process.
      */
-    public function reset()
+    public function reset(): void
     {
         foreach ($this->handlers as $handler) {
             if ($handler instanceof ResettableInterface) {