ROB: Deal with invalid Destinations

Issue: An
        AttributeError: 'NoneType' object has no attribute 'get_object'
    was raised when trying to write a page that was merged.

Fix: Guard IndirectObject.get_object access

Closes #997

PyPDF2/_merger.py

@@ -435,6 +435,8 @@ def _trim_outline(
             else:
                 prev_header_added = False
                 for j in range(*pages):
+                    if o["/Page"] is None:
+                        continue
                     if pdf.pages[j].get_object() == o["/Page"].get_object():
                         o[NameObject("/Page")] = o["/Page"].get_object()
                         new_outline.append(o)

PyPDF2/generic.py

@@ -218,7 +218,10 @@ def __init__(self, idnum: int, generation: int, pdf: Any) -> None:  # PdfReader
         self.pdf = pdf
 
     def get_object(self) -> Optional[PdfObject]:
-        return self.pdf.get_object(self).get_object()
+        obj = self.pdf.get_object(self)
+        if obj is None:
+            return None
+        return obj.get_object()
 
     def __repr__(self) -> str:
         return f"IndirectObject({self.idnum!r}, {self.generation!r})"

tests/test_generic.py

@@ -3,7 +3,7 @@
 
 import pytest
 
-from PyPDF2 import PdfReader, PdfWriter
+from PyPDF2 import PdfMerger, PdfReader, PdfWriter
 from PyPDF2.constants import TypFitArguments as TF
 from PyPDF2.errors import PdfReadError, PdfReadWarning, PdfStreamError
 from PyPDF2.generic import (
@@ -473,3 +473,21 @@ def test_bool_repr():
 
     # cleanup
     os.remove("tmp-fields-report.txt")
+
+
+def test_issue_997():
+    url = "https://github.com/py-pdf/PyPDF2/files/8908874/Exhibit_A-2_930_Enterprise_Zone_Tax_Credits_final.pdf"
+    name = "gh-issue-997.pdf"
+
+    merger = PdfMerger()
+    merged_filename = "tmp-out.pdf"
+    with pytest.warns(PdfReadWarning, match="not defined"):
+        merger.append(
+            BytesIO(get_pdf_from_url(url, name=name))
+        )  # here the error raises
+    with open(merged_filename, "wb") as f:
+        merger.write(f)
+    merger.close()
+
+    # cleanup
+    os.remove(merged_filename)