Add helper functions to deal with None

from pathlib import Path

from typing import Optional

from pypdf import PdfReader

    with PdfReader(pdf_path) as reader:

        fields = reader.get_fields()

    # TODO

    # for field, value in fields.items():

    #    print(field, "=", value)

    def f(name: str) -> Optional[str]:

        return fields[name].value if fields.get(name) else None

    def fs(*names: str) -> Optional[str]:

        values = (f(name) for name in names)

        return "\n".join(value for value in values if value) or None

    return PaymentOrder(

        petitioner_name=fields["Name"].value,

        petitioner_contact=fields["Kontaktdaten"].value,

        reference=fields["Text6"].value + "\n" + fields["Text7"].value,

        amount=parse_euro_amount(fields["Text8"].value),

        payee_name=fields["Text9"].value,

        payee_iban="DE" + fields["Text10"].value,

        payee_bic=fields["Text11"].value,

        budgetary_item_id=fields["Text12"].value,

        petitioner_name=f("Name"),

        petitioner_contact=f("Kontaktdaten"),

        reference=fs("Text6", "Text7"),

        amount=parse_euro_amount(f("Text8")),

        payee_name=f("Text9"),

        payee_iban="DE" + f("Text10"),

        payee_bic=f("Text11"),

        budgetary_item_id=f("Text12"),

    )