diff --git a/test/test_YoutubeDL.py b/test/test_YoutubeDL.py
index 8d796bcdd..c02bfadfc 100644
--- a/test/test_YoutubeDL.py
+++ b/test/test_YoutubeDL.py
@@ -664,15 +664,15 @@ def test_add_extra_info(self):
     }
 
     def test_prepare_outtmpl_and_filename(self):
-        def test(tmpl, expected, **params):
+        def test(tmpl, expected, *, info=None, **params):
             params['outtmpl'] = tmpl
             ydl = YoutubeDL(params)
             ydl._num_downloads = 1
             self.assertEqual(ydl.validate_outtmpl(tmpl), None)
 
-            outtmpl, tmpl_dict = ydl.prepare_outtmpl(tmpl, self.outtmpl_info)
+            outtmpl, tmpl_dict = ydl.prepare_outtmpl(tmpl, info or self.outtmpl_info)
             out = outtmpl % tmpl_dict
-            fname = ydl.prepare_filename(self.outtmpl_info)
+            fname = ydl.prepare_filename(info or self.outtmpl_info)
 
             if callable(expected):
                 self.assertTrue(expected(out))
@@ -700,6 +700,15 @@ def test(tmpl, expected, **params):
         test('%(width)06d.%%(ext)s', 'NA.%(ext)s')
         test('%%(width)06d.%(ext)s', '%(width)06d.mp4')
 
+        # ID sanitization
+        test('%(id)s', '_abcd', info={'id': '_abcd'})
+        test('%(some_id)s', '_abcd', info={'some_id': '_abcd'})
+        test('%(formats.0.id)s', '_abcd', info={'formats': [{'id': '_abcd'}]})
+        test('%(id)s', '-abcd', info={'id': '-abcd'})
+        test('%(id)s', '.abcd', info={'id': '.abcd'})
+        test('%(id)s', 'ab__cd', info={'id': 'ab__cd'})
+        test('%(id)s', ('ab:cd', 'ab -cd'), info={'id': 'ab:cd'})
+
         # Invalid templates
         self.assertTrue(isinstance(YoutubeDL.validate_outtmpl('%'), ValueError))
         self.assertTrue(isinstance(YoutubeDL.validate_outtmpl('%(title)'), ValueError))
diff --git a/yt_dlp/YoutubeDL.py b/yt_dlp/YoutubeDL.py
index f60b7eec9..bf3eef67b 100644
--- a/yt_dlp/YoutubeDL.py
+++ b/yt_dlp/YoutubeDL.py
@@ -934,7 +934,7 @@ def create_key(outer_mobj):
             fmt = outer_mobj.group('format')
             mobj = re.match(INTERNAL_FORMAT_RE, key)
             if mobj is None:
-                value, default = None, na
+                value, default, mobj = None, na, {'fields': ''}
             else:
                 mobj = mobj.groupdict()
                 default = mobj['default'] if mobj['default'] is not None else na
@@ -944,7 +944,6 @@ def create_key(outer_mobj):
                 fmt = '0{:d}d'.format(field_size_compat_map[key])
 
             value = default if value is None else value
-            key += '\0%s' % fmt
 
             if fmt == 'c':
                 value = compat_str(value)
@@ -962,7 +961,8 @@ def create_key(outer_mobj):
                     # So we convert it to repr first
                     value, fmt = repr(value), '%ss' % fmt[:-1]
                 if fmt[-1] in 'csr':
-                    value = sanitize(key, value)
+                    value = sanitize(mobj['fields'].split('.')[-1], value)
+            key += '\0%s' % fmt
             TMPL_DICT[key] = value
             return '%({key}){fmt}'.format(key=key, fmt=fmt)
 
diff --git a/yt_dlp/utils.py b/yt_dlp/utils.py
index 59445a1da..8e85620cc 100644
--- a/yt_dlp/utils.py
+++ b/yt_dlp/utils.py
@@ -6241,6 +6241,8 @@ def traverse_obj(obj, keys, *, casesense=True, is_user_input=False, traverse_str
             if is_user_input:
                 key = (int_or_none(key) if ':' not in key
                        else slice(*map(int_or_none, key.split(':'))))
+                if key is None:
+                    return None
             if not isinstance(obj, (list, tuple)):
                 if traverse_string:
                     obj = compat_str(obj)