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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 create_contact(self, email=None, first_name=None, last_name=None, phone_number=None):
 """ Create a contant which is later passed to payment. """

        result = {}
        if email:
            result['email'] = email
        if first_name is not None:
            result['first_name'] = first_name
        if last_name is not None:
            result['last_name'] = last_name
        if phone_number is not None:
            result['phone_number'] = phone_number
        return result if len(result) > 0 else None