@@ -575,11 +575,14 @@ def _iter_from_process_or_stream(cls, repo: "Repo", proc_or_stream: Union[Popen,
 
         if hasattr(proc_or_stream, "wait"):
             proc_or_stream = cast(Popen, proc_or_stream)
-            if proc_or_stream.stdout is not None:
-                stream = proc_or_stream.stdout
+            stream = proc_or_stream.stdout
+            if stream is None:
+                raise ValueError("Process has no stdout stream")
         elif hasattr(proc_or_stream, "readline"):
             proc_or_stream = cast(IO, proc_or_stream)  # type: ignore[redundant-cast]
             stream = proc_or_stream
+        else:
+            raise TypeError("Expected a process or stream")
 
         readline = stream.readline
         while True:
 
@@ -7,6 +7,7 @@
 
 import git
 from git.exc import InvalidGitRepositoryError
+from git.util import IterableList
 
 from .base import Submodule, UpdateProgress
 from .util import find_first_remote_branch
@@ -19,7 +20,6 @@
 
 if TYPE_CHECKING:
     from git.repo import Repo
-    from git.util import IterableList
 
 # ----------------------------------------------------------------------------
 
@@ -162,6 +162,7 @@ def update(  # type: ignore[override]
             prefix = "DRY-RUN: "
 
         repo = self.repo
+        sms: "IterableList[Submodule]" = IterableList("name")
 
         try:
             # SETUP BASE COMMIT
@@ -182,7 +183,7 @@ def update(  # type: ignore[override]
             # END handle previous commit
 
             psms: "IterableList[Submodule]" = self.list_items(repo, parent_commit=previous_commit)
-            sms: "IterableList[Submodule]" = self.list_items(repo)
+            sms = self.list_items(repo)
             spsms = set(psms)
             ssms = set(sms)
 
 
@@ -327,6 +327,11 @@ def test_rev_list_bisect_all(self):
         for sha1, commit in zip(expected_ids, commits):
             self.assertEqual(sha1, commit.hexsha)
 
+    def test_iter_from_invalid_process_or_stream(self):
+        for source, error in ((Mock(wait=Mock(), stdout=None), ValueError), (object(), TypeError)):
+            with self.assertRaises(error):
+                list(Commit._iter_from_process_or_stream(self.rorepo, source))
+
     @with_rw_directory
     def test_ambiguous_arg_iteration(self, rw_dir):
         rw_repo = Repo.init(osp.join(rw_dir, "test_ambiguous_arg"))
 
@@ -511,6 +511,9 @@ def test_root_module(self, rwrepo):
         # Cannot set the parent commit as root module's path didn't exist.
         self.assertRaises(ValueError, rm.set_parent_commit, "HEAD")
 
+        with mock.patch.object(RootModule, "list_items", side_effect=ValueError("boom")):
+            rm.update(keep_going=True)
+
         # TEST UPDATE
         #############
         # Set up a commit that removes existing, adds new and modifies existing