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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 list(cls, session, first_name=None, last_name=None, email=None, modified_since=None):
 """List the customers. Customers can be filtered on any combination of first name, last name, email, and modifiedSince. Args: session (requests.sessions.Session):
 Authenticated session. first_name (str, optional):
 First name of customer. last_name (str, optional):
 Last name of customer. email (str, optional):
 Email address of customer. modified_since (datetime.datetime, optional):
 If modified after this date. Returns: RequestPaginator(output_type=helpscout.models.Customer):
 Customers iterator. """

        return super(Customers, cls).list(
            session,
            data=cls.__object__.get_non_empty_vals({
                'firstName': first_name,
                'lastName': last_name,
                'email': email,
                'modifiedSince': modified_since,
            })
        )