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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 _remove_nulls(managed_clusters):
 """ Remove some often-empty fields from a list of ManagedClusters, so the JSON representation doesn't contain distracting null fields. This works around a quirk of the SDK for python behavior. These fields are not sent by the server, but get recreated by the CLI's own "to_dict" serialization. """

    attrs = ['tags']
    ap_attrs = ['os_disk_size_gb', 'vnet_subnet_id']
    sp_attrs = ['secret']
    for managed_cluster in managed_clusters:
        for attr in attrs:
            if getattr(managed_cluster, attr, None) is None:
                delattr(managed_cluster, attr)
        for ap_profile in managed_cluster.agent_pool_profiles:
            for attr in ap_attrs:
                if getattr(ap_profile, attr, None) is None:
                    delattr(ap_profile, attr)
        for attr in sp_attrs:
            if getattr(managed_cluster.service_principal_profile, attr, None) is None:
                delattr(managed_cluster.service_principal_profile, attr)
    return managed_clusters