additional Feature after episodes

[KeplerC]

Describe the bug
the additional features becomes null and count as 0

{"episode_id":0,"Finished":true,"feature_arm_view_type":"str","feature_arm_view_shape":"()","arm_view_count":1,"collector":null,"feature_gripper_closedness_action_type":null,"feature_gripper_closedness_action_shape":null,"gripper_closedness_action_count":null,"feature_rotation_delta_type":null,"feature_rotation_delta_shape":null,"rotation_delta_count":null,"feature_terminate_episode_type":null,"feature_terminate_episode_shape":null,"terminate_episode_count":null,"feature_world_vector_type":null,"feature_world_vector_shape":null,"world_vector_count":null,"feature_is_first_type":null,"feature_is_first_shape":null,"is_first_count":null,"feature_is_last_type":null,"feature_is_last_shape":null,"is_last_count":null,"feature_is_terminal_type":null,"feature_is_terminal_shape":null,"is_terminal_count":null,"feature_hand_image_type":null,"feature_hand_image_shape":null,"hand_image_count":null,"feature_image_type":null,"feature_image_shape":null,"image_count":null,"feature_image_with_depth_type":null,"feature_image_with_depth_shape":null,"image_with_depth_count":null,"feature_natural_language_embedding_type":null,"feature_natural_language_embedding_shape":null,"natural_language_embedding_count":null,"feature_natural_language_instruction_type":null,"feature_natural_language_instruction_shape":null,"natural_language_instruction_count":null,"feature_robot_state_type":null,"feature_robot_state_shape":null,"robot_state_count":null,"feature_reward_type":null,"feature_reward_shape":null,"reward_count":null}
{"episode_id":1,"Finished":true,"feature_arm_view_type":"str","feature_arm_view_shape":"()","arm_view_count":0,"collector":"User 2","feature_gripper_closedness_action_type":"float32","feature_gripper_closedness_action_shape":"()","gripper_closedness_action_count":0,"feature_rotation_delta_type":"float32","feature_rotation_delta_shape":"(3,)","rotation_delta_count":0,"feature_terminate_episode_type":"float32","feature_terminate_episode_shape":"()","terminate_episode_count":0,"feature_world_vector_type":"float32","feature_world_vector_shape":"(3,)","world_vector_count":0,"feature_is_first_type":"bool","feature_is_first_shape":"()","is_first_count":0,"feature_is_last_type":"bool","feature_is_last_shape":"()","is_last_count":0,"feature_is_terminal_type":"bool","feature_is_terminal_shape":"()","is_terminal_count":0,"feature_hand_image_type":"uint8","feature_hand_image_shape":"(480, 640, 3)","hand_image_count":0,"feature_image_type":"uint8","feature_image_shape":"(480, 640, 3)","image_count":0,"feature_image_with_depth_type":"float32","feature_image_with_depth_shape":"(480, 640, 1)","image_with_depth_count":0,"feature_natural_language_embedding_type":"float32","feature_natural_language_embedding_shape":"(512,)","natural_language_embedding_count":0,"feature_natural_language_instruction_type":"string","feature_natural_language_instruction_shape":"()","natural_language_instruction_count":0,"feature_robot_state_type":"float32","feature_robot_state_shape":"(15,)","robot_state_count":0,"feature_reward_type":"float32","feature_reward_shape":"()","reward_count":0}

To Reproduce
slightly explore the introduction experiment:

import fog_x

# 🦊 Dataset Creation 
# from distributed dataset storage 
dataset = fog_x.Dataset(
    name="demo_ds",
    path="~/test_dataset", # can be AWS S3, Google Bucket! 
)  

# 🦊 Data collection: 
# create a new trajectory
episode = dataset.new_episode()
# collect step data for the episode
episode.add(feature = "arm_view", value = "image1.jpg")
# Automatically time-aligns and saves the trajectory
episode.close()

# 🦊 Data Loading:
# load from existing RT-X/Open-X datasets
dataset.load_rtx_episodes(
    name="berkeley_autolab_ur5",
    split = "train[:2]",
    additional_metadata={"collector": "User 2"}
)

# 🦊 Data Management and Analytics: 
# Compute and memory efficient filter, map, aggregate, groupby
episode_info = dataset.get_episode_info()
desired_episodes = episode_info.filter(episode_info["collector"] == "User 2")

Expected behavior
A clear and concise description of what you expected to happen.

Screenshots
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Desktop (please complete the following information):

• OS: [e.g. iOS]
• Version [e.g. 22]

Additional context
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