Fixed http_build_query() deprecation warning

Author: fastnloud

CHANGELOG.md

@@ -3,6 +3,7 @@
 ## 4.1.1
 
 * Changed PHP version constraint to >=7.4
+* Fixed http_build_query() deprecation warning: Passing null to parameter #2 ($numeric_prefix) of type string is deprecated
 
 ## 4.0.1
 

lib/FH/PostcodeAPI/Client.php

@@ -121,7 +121,7 @@ private function buildUrl(string $path): string
 
     private function createHttpGetRequest(string $url, array $params = []): Request
     {
-        $url .= (count($params) > 0 ? '?' . http_build_query($params, null, '&', PHP_QUERY_RFC3986) : '');
+        $url .= (count($params) > 0 ? '?' . http_build_query($params, '', '&', PHP_QUERY_RFC3986) : '');
 
         return new Request('GET', $url);
     }