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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _merge_observation(accum_observation, observation):
 """ Old visual observation is discarded, because it is outdated frame. Text observations are merged, because they are messages sent from the rewarder. """

    if observation is None:
        # We're currently masking. So accum_observation probably
        # belongs to the previous episode. We may lose a "text"
        # observation from the previous episode, but that's ok.
        return None
    elif accum_observation is None:
        # Nothing to merge together
        return observation

    accum_observation['vision'] = observation.get('vision')
    accum_observation['text'] = accum_observation.get('text', []) + observation.get('text', [])
    return accum_observation