ROB: Skip destination page being None in PdfWriter (#2963)

Some PDFs happen `dest["/Page"] is None` which causes 

> AttributeError: 'NoneType' object has no attribute 'indirect_reference'

when merging files.

pypdf/_writer.py

@@ -2758,7 +2758,7 @@ def _process_named_dests(dest: Any) -> None:
             ):
                 # already exists : should not duplicate it
                 pass
-            elif isinstance(dest["/Page"], NullObject):
+            elif dest["/Page"] is None or isinstance(dest["/Page"], NullObject):
                 pass
             elif isinstance(dest["/Page"], int):
                 # the page reference is a page number normally not a PDF Reference

tests/test_writer.py

@@ -2484,6 +2484,16 @@ def test_append_pdf_with_dest_without_page(caplog):
     assert len(writer.named_destinations) == 3
 
 
+@pytest.mark.enable_socket
+def test_destination_page_is_none():
+    """Tests for #2963"""
+    url = "https://github.com/user-attachments/files/17879461/3.pdf"
+    name = "iss2963.pdf"
+    reader = PdfReader(BytesIO(get_data_from_url(url, name=name)))
+    writer = PdfWriter()
+    writer.append(reader)
+
+
 def test_stream_not_closed():
     """Tests for #2905"""
     src = RESOURCE_ROOT / "pdflatex-outline.pdf"