Make gpu and agent nullable in doc for task from agent update and retrieve

arkindex/ponos/serializers.py

@@ -137,8 +137,8 @@ class TaskSerializer(TaskLightSerializer):
 
     logs = serializers.CharField(source="short_logs", read_only=True)
     full_log = serializers.URLField(source="s3_logs_get_url", read_only=True)
-    agent = AgentLightSerializer(read_only=True)
-    gpu = GPUSerializer(read_only=True)
+    agent = AgentLightSerializer(read_only=True, allow_null=True)
+    gpu = GPUSerializer(read_only=True, allow_null=True)
     extra_files = serializers.DictField(read_only=True)
 
     class Meta(TaskLightSerializer.Meta):