def transform_feature_on_popularity(feature: str, feature_popularity: dict) -> str:
    """
    INPUT
    feature - any categorical feauture (e.g., Developer, full-stack; Developer, back-end)
    feature_popularity - a dictionary mapping the feature to popularity
    OUTPUT
    transformed feature - the more popular feature value (e.g., Developer, full-stack)
    """

    feature_types = feature.split(';')
    max_pop = -1
    popular_feature_type = 'None'

    for r in feature_types:
        pop = feature_popularity.get(r, -1)

        if pop > max_pop:
            popular_feature_type = r
            max_pop = pop

    return popular_feature_type