draw_string() is not clear in PythonAPI world.debug..clear_debug_shape()

[donghaiwang]

Setup
Describe the setup you are using to run CARLA along with its version:

• CARLA version: 0.9.15 ue4-dev lastest
• Platform: windows 10
• Python version: 3.7
• GPU: RTX3090

Describe the bug
draw_box() will clear. However, draw_string() is not clear in PythonAPI world.debug..clear_debug_shape()

Scripts

import time

import carla
import random

# 连接到客户端并获取世界对象
client = carla.Client('localhost', 2000)
world = client.get_world()

# 我们还将设置观察者，这样我们就可以看到我们在做什么
spectator = world.get_spectator()

spawn_points = world.get_map().get_spawn_points()

# 将观察者移动到俯视图
transform = carla.Transform(spawn_points[0].transform(carla.Location(x=-4, z=100)), carla.Rotation(yaw=-180, pitch=-90))
spectator.set_transform(transform)

debug_helper = world.debug

# 在地图上用数字标出生成点的位置
for i, spawn_point in enumerate(spawn_points):
    debug_helper.draw_string(spawn_point.location, str(i), life_time=15)  #


debug = world.debug
world_snapshot = world.get_snapshot()

for actor_snapshot in world_snapshot:
    actual_actor = world.get_actor(actor_snapshot.id)
    if actual_actor.type_id == 'traffic.traffic_light':
        debug.draw_box(carla.BoundingBox(actor_snapshot.get_transform().location,carla.Vector3D(0.5,0.5,2)),actor_snapshot.get_transform().rotation, 0.05, carla.Color(255,0,0,0),0)
# ...

time.sleep(3)
# 清除调式时的绘制信息
debug_helper.clear_debug_shape()

Screenshots

[Blyron]

What is the expected the result?

[donghaiwang]

Should the graphic string drawn by draw_string() disappear after calling the method world.debug.clear_debug_shape()?

[Blyron]

PR ready to get this