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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 update_nb_metadata(nb_path=None, title=None, summary=None, keywords='fastai', overwrite=True, **kwargs):
    "Creates jekyll metadata for given notebook path."
    nb = read_nb(nb_path)
    data = {'title': title, 'summary': summary, 'keywords': keywords, **kwargs}
    data = {k:v for (k,v) in data.items() if v is not None} # remove none values
    if not data: return
    nb['metadata']['jekyll'] = data
    write_nb(nb, nb_path)
    NotebookNotary().sign(nb)