BUG: images property fails if NullObject in list (#2215)

Discovered while working on #2214

pypdf/_page.py

@@ -83,6 +83,7 @@
     NullObject,
     NumberObject,
     RectangleObject,
+    StreamObject,
 )
 
 MERGE_CROP_BOX = "cropbox"  # pypdf<=3.4.0 used 'trimbox'
@@ -509,6 +510,8 @@ def _get_ids_image(
 
         x_object = obj[PG.RESOURCES][RES.XOBJECT].get_object()  # type: ignore
         for o in x_object:
+            if not isinstance(x_object[o], StreamObject):
+                continue
             if x_object[o][IA.SUBTYPE] == "/Image":
                 lst.append(o if len(ancest) == 0 else ancest + [o])
             else:  # is a form with possible images inside

tests/test_images.py

@@ -12,8 +12,8 @@
 import pytest
 from PIL import Image, ImageChops, ImageDraw
 
-from pypdf import PdfReader
-from pypdf._page import PageObject
+from pypdf import PageObject, PdfReader
+from pypdf.generic import NameObject, NullObject
 
 from . import get_data_from_url
 
@@ -218,4 +218,5 @@ def test_loop_in_image_keys():
     url = "https://github.com/py-pdf/pypdf/files/12309492/example_134.pdf"
     name = "iss2077.pdf"
     reader = PdfReader(BytesIO(get_data_from_url(url, name=name)))
+    reader.pages[0]["/Resources"]["/XObject"][NameObject("/toto")] = NullObject()
     reader.pages[0].images.keys()