diff --git a/phpstan.neon b/phpstan.neon
index e9e666d..ffc7ccf 100644
--- a/phpstan.neon
+++ b/phpstan.neon
@@ -1,5 +1,6 @@
 parameters:
-	level: 5
+	level: 8
+	checkMissingIterableValueType: false
 	errorFormat: raw
 
 	paths:
diff --git a/src/Schema/Message.php b/src/Schema/Message.php
index ac7eeda..4e976d0 100644
--- a/src/Schema/Message.php
+++ b/src/Schema/Message.php
@@ -9,6 +9,8 @@
 
 namespace Nette\Schema;
 
+use Nette;
+
 
 final class Message
 {
@@ -91,6 +93,6 @@ public function toString(): string
 		return preg_replace_callback('~( ?)%(\w+)%~', function ($m) use ($vars) {
 			[, $space, $key] = $m;
 			return $vars[$key] === null ? '' : $space . $vars[$key];
-		}, $this->message);
+		}, $this->message) ?? throw new Nette\InvalidStateException(preg_last_error_msg());
 	}
 }
diff --git a/src/Schema/Processor.php b/src/Schema/Processor.php
index 073c17b..3290ba6 100644
--- a/src/Schema/Processor.php
+++ b/src/Schema/Processor.php
@@ -18,7 +18,7 @@
 final class Processor
 {
 	public array $onNewContext = [];
-	private ?Context $context;
+	private Context $context;
 	private bool $skipDefaults = false;