ROB: Let PdfWriter.merge cope with missing "/Fields" (#1628)

Fixes #1627

pypdf/_writer.py

@@ -2618,13 +2618,16 @@ def merge(
                     cast(DictionaryObject, self._root_object["/AcroForm"])["/Fields"],
                 )
             trslat = self._id_translated[id(reader)]
-            for f in reader.trailer["/Root"]["/AcroForm"]["/Fields"]:  # type: ignore
-                try:
-                    ind = IndirectObject(trslat[f.idnum], 0, self)
-                    if ind not in arr:
-                        arr.append(ind)
-                except KeyError:
-                    pass
+            try:
+                for f in reader.trailer["/Root"]["/AcroForm"]["/Fields"]:  # type: ignore
+                    try:
+                        ind = IndirectObject(trslat[f.idnum], 0, self)
+                        if ind not in arr:
+                            arr.append(ind)
+                    except KeyError:  # for trslat[] which mean the field has not be copied through the page
+                        pass
+            except KeyError:  # for /Acroform or /Fields are not existing
+                arr = self._add_object(ArrayObject())
             cast(DictionaryObject, self._root_object["/AcroForm"])[
                 NameObject("/Fields")
             ] = arr

tests/test_writer.py

@@ -740,14 +740,30 @@ def test_sweep_indirect_references_nullobject_exception():
 
 @pytest.mark.external
 @pytest.mark.slow
-def test_write_outline_item_on_page_fitv():
-    url = "https://corpora.tika.apache.org/base/docs/govdocs1/922/922840.pdf"
-    name = "tika-922840.pdf"
+@pytest.mark.parametrize(
+    ("url", "name"),
+    [
+        (
+            "https://corpora.tika.apache.org/base/docs/govdocs1/924/924666.pdf",
+            "test_sweep_indirect_references_nullobject_exception.pdf",
+        ),
+        (
+            "https://corpora.tika.apache.org/base/docs/govdocs1/922/922840.pdf",
+            "test_write_outline_item_on_page_fitv.pdf",
+        ),
+        ("https://github.com/py-pdf/pypdf/files/10715624/test.pdf", "iss1627.pdf"),
+    ],
+)
+def test_some_appends(url, name):
     reader = PdfReader(BytesIO(get_pdf_from_url(url, name=name)))
+    # PdfMerger
     merger = PdfMerger()
     merger.append(reader)
     merger.write("tmp-merger-do-not-commit.pdf")
-
+    # PdfWriter
+    merger = PdfWriter()
+    merger.append(reader)
+    merger.write("tmp-merger-do-not-commit.pdf")
     # cleanup
     os.remove("tmp-merger-do-not-commit.pdf")