Add PHPstan and fix all checks for max level

src/Response/CancelResponse.php

@@ -28,31 +28,26 @@ class CancelResponse
 	/**
 	 * Amazon Gift Card Raw JSON
 	 *
-	 * @var string
+	 * @var array<mixed>
 	 */
 	protected $raw_json;
-	/**
-	 * @var array
-	 */
-	protected $log;
 
 	/**
 	 * Response constructor.
-	 * @param array $json_response
+	 * @param array<mixed> $json_response
 	 */
 	public function __construct(array $json_response)
 	{
 		$this->raw_json = $json_response;
-		$this->log = AmazonDebug::getLog(AmazonDebug::getId());
 		$this->parseJsonResponse($json_response);
 	}
 
 	/**
-	 * @return array
+	 * @return array<mixed>
 	 */
 	public function getLog(): array
 	{
-		return $this->log;
+		return AmazonDebug::getLog(AmazonDebug::getId());
 	}
 
 	/**
@@ -84,11 +79,11 @@ class CancelResponse
 	 */
 	public function getRawJson(): string
 	{
-		return json_encode($this->raw_json);
+		return (json_encode($this->raw_json)) ?: '';
 	}
 
 	/**
-	 * @param  array $json_response
+	 * @param  array<mixed> $json_response
 	 * @return CancelResponse
 	 */
 	public function parseJsonResponse(array $json_response): self