pikepdf: pikepdf._qpdf.PdfError on a specific PDF file with pikepdf >= 4.5.0

Hi, I have a bug with a specific PDF (which I can’t publish unfortunately).

The error is the following:

Traceback (most recent call last):
  File "/tests/test_pikepdf.py", line 10, in test_pikepdf
    pdf.save("/tmp/toto.pdf")
  File "/usr/local/lib/python3.8/site-packages/pikepdf/_methods.py", line 774, in save
    self._save(
pikepdf._qpdf.PdfError: operation for dictionary attempted on object of type null: returning null for attempted key retrieval

It happens with this python code, on the save statement:

import pikepdf
from pathlib import Path
fpath = Path("tests/fixtures/scanned_rotation.pdf")
pdf = pikepdf.Pdf.open(fpath)
pdf.save("/tmp/toto.pdf")

This is my Dockerfile to reproduce the problem:

FROM tiangolo/uvicorn-gunicorn-fastapi:python3.8
RUN apt-get update -q -y && apt-get upgrade -q -y
RUN python -m pip install --upgrade pip
RUN pip install --no-cache-dir install pikepdf
COPY app /app
COPY tests /tests
WORKDIR /app

It worked until pikepdf version 4.4.1 but from 4.5.0 to current version (5.0.1) it raises this pikepdf._qpdf.PdfError exception.

Thank you for your help and support