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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 get_next_url(request, redirect_field_name):
 """Retrieves next url from request Note: This verifies that the url is safe before returning it. If the url is not safe, this returns None. :arg HttpRequest request: the http request :arg str redirect_field_name: the name of the field holding the next url :returns: safe url or None """

    next_url = request.GET.get(redirect_field_name)
    if next_url:
        kwargs = {
            'url': next_url,
            'require_https': import_from_settings(
                'OIDC_REDIRECT_REQUIRE_HTTPS', request.is_secure())
        }

        hosts = list(import_from_settings('OIDC_REDIRECT_ALLOWED_HOSTS', []))
        hosts.append(request.get_host())
        kwargs['allowed_hosts'] = hosts

        is_safe = is_safe_url(**kwargs)
        if is_safe:
            return next_url
    return None