make some property optional

src/Contracts/PaymentGatewayDriver.php

 
     public function verifyGatewayCallback(Request $request, Response &$response = null): bool;
 
-    public function getBillIdFromRequest(Request $request): string;
+    public function getBillIdFromRequest(Request $request): ?string;
 
-    public function getBillStatus(Request $request): int;
+    public function getBillStatus(Request $request): ?int;
 
-    public function isBillSuccess(Request $request): bool;
+    public function isBillSuccess(Request $request): ?bool;
 
-    public function isBillFailed(Request $request): bool;
+    public function isBillFailed(Request $request): ?bool;
 
-    public function isBillPending(Request $request): bool;
+    public function isBillPending(Request $request): ?bool;
 }

src/Traits/BillStatusBoolean.php

 
 trait BillStatusBoolean
 {
-    public function isBillSuccess(Request $request): bool
+    public function isBillSuccess(Request $request): ?bool
     {
-        return $this->getBillStatus($request) > 0;
+        $status = $this->getBillStatus($request);
+        return $status === null ? null : $status > 0;
     }
 
-    public function isBillFailed(Request $request): bool
+    public function isBillFailed(Request $request): ?bool
     {
-        return $this->getBillStatus($request) < 0;
+        $status = $this->getBillStatus($request);
+        return $status === null ? null : $status < 0;
     }
 
-    public function isBillPending(Request $request): bool
+    public function isBillPending(Request $request): ?bool
     {
-        return $this->getBillStatus($request) == 0;
+        $status = $this->getBillStatus($request);
+        return $status === null ? null : $status == 0;
     }
 }