How to use the pyserini.collection.Cord19Article function in pyserini

def main(path, coef, top):
    documents_with_text = dict()
    documents_without_text = dict()
    documents_zero_abs = dict()
    documents_empty_body = dict()

    cnt = 0
    collection = Collection('Cord19AbstractCollection', path)
    articles = collection.__next__()

    # iterate through raw collection
    for (i, d) in enumerate(articles):
        article = Cord19Article(d.raw)
        # documents with empty abstract
        if len(article.abstract()) == 0:
            documents_zero_abs.setdefault(article.cord_uid(), [])
            documents_zero_abs[article.cord_uid()].append(article.metadata()["doi"])
        else:
            # document does not have text
            if not article.is_full_text():
                documents_without_text.setdefault(article.cord_uid(), [])
                documents_without_text[article.cord_uid()].append(article.metadata()["doi"])
                documents_without_text[article.cord_uid()].append(len(article.title()))
                documents_without_text[article.cord_uid()].append(len(article.abstract()))
            # document whose text body is empty
            elif len(article.body()) == 0:
                documents_empty_body.setdefault(article.cord_uid(), [])
                documents_empty_body[article.cord_uid()].append(article.metadata()["doi"])
            # normal document and we save for analysis later