KeyError '/Opt' in get_fields

[alesdotio]

Replace this: What happened? What were you trying to achieve?

Trying to get the fields out of a PDF.

Environment

Which environment were you using when you encountered the problem?

$ python -m platform
macOS-14.6.1-arm64-arm-64bit

$ python -c "import pypdf;print(pypdf._debug_versions)"
pypdf==4.3.1, crypt_provider=('pycryptodome', '3.20.0'), PIL=10.4.0

Code + PDF

This is a minimal, complete example that shows the issue:

reader = PdfReader(pdf)
fields = reader.get_fields()

Share here the PDF file(s) that cause the issue. The smaller they are, the
better. Let us know if we may add them to our tests!

Unfortunately, I cannot share the PDF.

Traceback

This is the complete traceback I see:

    fields = reader.get_fields()
../../.venv/lib/python3.12/site-packages/pypdf/_doc_common.py:533: in get_fields
    self._build_field(field, retval, fileobj, field_attributes, stack)
../../.venv/lib/python3.12/site-packages/pypdf/_doc_common.py:570: in _build_field
    retval[key][NameObject("/_States_")] = obj[NameObject(FA.Opt)]
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = {'/DA': '/AgencyFB 8 Tf 0 g', '/FT': '/Ch', '/Ff': 917504, '/Kids': [IndirectObject(2453, 0, 4403691248), IndirectObject(2235, 0, 4403691248)], '/T': 'Designation', '/V': 'Town'}
key = '/Opt'

    def __getitem__(self, key: Any) -> PdfObject:
>       return dict.__getitem__(self, key).get_object()
E       KeyError: '/Opt'

../../.venv/lib/python3.12/site-packages/pypdf/generic/_data_structures.py:417: KeyError

Changing this line in _doc_common.py:570 fixes the problem for my case, but I have no idea what the consequences are:

        if obj.get(FA.FT, "") == "/Ch" and obj.get(NameObject(FA.Opt)):
            retval[key][NameObject("/_States_")] = obj[NameObject(FA.Opt)]

[pubpub-zz]

@alesdotio
Without data we can not complete an anamlysis.
I see 2 options to try to go forward:
a) take an empty copy of the form, check if the error is still present and provide us with
b) send privately a copy to @stefan6419846 : we promise to not disclose the data

[pubpub-zz]

@alesdotio
Is this approach OK for you ? else we will have to close this as analysis can not be done

[alesdotio]

@alesdotio Is this approach OK for you ? else we will have to close this as analysis can not be done

Yeah, that's fair. I will try to reproduce it on another file and reopen the issue if I manage.

My guess is that this is a choice field without any choices defined?

[pubpub-zz]

@alesdotio any update ?