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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 to_json(payload, mode="history"):
 """Converts all keys in a potentially nested array into their JSON representation"""

    for key, val in six.iteritems(payload):
        if isinstance(val, dict):
            payload[key] = to_json(val, mode)
        else:
            payload[key] = val_to_json(
                key, val, mode, step=payload.get("_step"))
    return payload