fix(rules): Serializers

Added small changes

modules/rule/src/test/scala/de/nowchess/rules/json/JsonSerializersTest.scala

@@ -32,11 +32,13 @@ class JsonSerializersTest extends AnyFunSuite with Matchers:
 
   // ── SquareKeyDeserializer ─────────────────────────────────────────
 
+  // scalafix:off DisableSyntax.null
   test("SquareKeyDeserializer returns square for valid key"):
     new SquareKeyDeserializer().deserializeKey("e4", null) shouldBe e4
 
   test("SquareKeyDeserializer returns null for invalid key"):
     new SquareKeyDeserializer().deserializeKey("z9", null) shouldBe null
+  // scalafix:on DisableSyntax.null
 
   // ── SquareSerializer/Deserializer ─────────────────────────────────
 
@@ -46,8 +48,10 @@ class JsonSerializersTest extends AnyFunSuite with Matchers:
   test("SquareDeserializer reads valid square string"):
     mapper.readValue(""""e4"""", classOf[Square]) shouldBe e4
 
+  // scalafix:off DisableSyntax.null
   test("SquareDeserializer returns null for invalid square string"):
     mapper.readValue(""""z9"""", classOf[Square]) shouldBe null
+  // scalafix:on DisableSyntax.null
 
   // ── MoveTypeSerializer ────────────────────────────────────────────