some improvements

src/TaskManager.php

@@ -33,6 +33,11 @@ class TaskManager
      */
     private $tasks = [];
 
+    /**
+     * @var Serializer
+     */
+    private $serializer;
+
     /**
      * @param Taskwarrior $taskwarrior
      */
@@ -400,12 +405,16 @@ class TaskManager
      */
     private function getSerializer()
     {
+        if ($this->serializer) {
+            return $this->serializer;
+        }
+
         $propertyNamingStrategy = new SerializedNameAnnotationStrategy(new CamelCaseNamingStrategy());
 
         $visitor = new JsonSerializationVisitor($propertyNamingStrategy);
         $visitor->setOptions(JSON_UNESCAPED_UNICODE);
 
-        return SerializerBuilder::create()
+        return $this->serializer = SerializerBuilder::create()
             ->setPropertyNamingStrategy($propertyNamingStrategy)
             ->configureHandlers(function (HandlerRegistryInterface $registry) {
                 $registry->registerSubscribingHandler(new CarbonHandler());

src/Taskwarrior.php

@@ -38,6 +38,7 @@ class Taskwarrior
      * @param string $taskData
      * @param array $rcOptions
      * @param string $bin
+     * @throws TaskwarriorException
      */
     public function __construct($taskrc = '~/.taskrc', $taskData = '~/.task', $rcOptions = [], $bin = 'task')
     {
@@ -51,6 +52,10 @@ class Taskwarrior
             ),
             $rcOptions
         );
+
+        if (version_compare($this->version(), '2.4.3') < 0) {
+            throw new TaskwarriorException(sprintf("Taskwarrior version %s isn't supported", $this->version()));
+        }
     }
 
     /**