SCA: simplify some ifs in favour of null coalescing operator

Author: kalessil

Generator/UrlGenerator.php

@@ -254,10 +254,7 @@ protected function doGenerate($variables, $defaults, $requirements, $tokens, $pa
         });
 
         // extract fragment
-        $fragment = '';
-        if (isset($defaults['_fragment'])) {
-            $fragment = $defaults['_fragment'];
-        }
+        $fragment = $defaults['_fragment'] ?? '';
 
         if (isset($extra['_fragment'])) {
             $fragment = $extra['_fragment'];