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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 version(request):
 """ Returns the contents of version.json or a 404. """

    version_json = import_string(version_callback)(settings.BASE_DIR)
    if version_json is None:
        return HttpResponseNotFound('version.json not found')
    else:
        return JsonResponse(version_json)