Fixed TypeError in Regex strategy when expression evaluates to null.

Author: Bilge

src/Strategy/Regex.php

@@ -18,7 +18,7 @@ public function __construct(
 
     public function __invoke($data, $context = null)
     {
-        if (preg_match($this->regex, parent::__invoke($data, $context), $matches)) {
+        if (preg_match($this->regex, parent::__invoke($data, $context) ?? '', $matches)) {
             if (is_array($this->capturingGroup)) {
                 return array_values(array_intersect_key($matches, array_flip($this->capturingGroup)));
             }

test/Unit/Mapper/Strategy/RegexTest.php

@@ -29,4 +29,11 @@ public function testRegexMatchArray(): void
 
         self::assertSame(['Alfa', 'Charlie'], $regex([]));
     }
+
+    public function testRegexMatchNullExpression(): void
+    {
+        $regex = (new Regex(null, '[Alfa]'))->setMapper(MockFactory::mockMapperEcho());
+
+        self::assertNull($regex([]));
+    }
 }