diff --git a/src/PhpPact/Standalone/ProviderVerifier/Model/Selector/Selector.php b/src/PhpPact/Standalone/ProviderVerifier/Model/Selector/Selector.php
index 31910832..476337f3 100644
--- a/src/PhpPact/Standalone/ProviderVerifier/Model/Selector/Selector.php
+++ b/src/PhpPact/Standalone/ProviderVerifier/Model/Selector/Selector.php
@@ -32,6 +32,6 @@ public function __construct(
      */
     public function jsonSerialize(): array
     {
-        return array_filter(get_object_vars($this), fn (null|string|bool $value) => null !== $value);
+        return array_filter(get_object_vars($this), fn (mixed $value) => is_bool($value) || is_string($value));
     }
 }