def features_properties_null_remove(obj):
    """
    Remove any properties of features in the collection that have 
    entries mapping to a null (i.e., None) value
    """
    features = obj['features']
    for i in tqdm(range(len(features))):
        if 'properties' in features[i]:
            properties = features[i]['properties']
            features[i]['properties'] = {p:properties[p] for p in properties if properties[p] is not None}
    return obj