diff --git a/nbgrader/apps/baseapp.py b/nbgrader/apps/baseapp.py
index ab115149..825cc8ae 100644
--- a/nbgrader/apps/baseapp.py
+++ b/nbgrader/apps/baseapp.py
@@ -211,17 +211,6 @@ class NbGrader(JupyterApp):
             cfg.Exchange.merge(cfg.TransferApp)
             del cfg.TransferApp
 
-        if 'BaseNbConvertApp' in cfg:
-            self.log.warning(
-                "Use BaseConverter in config, not BaseNbConvertApp. Outdated config:\n%s",
-                '\n'.join(
-                    'BaseNbConvertApp.{key} = {value!r}'.format(key=key, value=value)
-                    for key, value in cfg.BaseNbConvertApp.items()
-                )
-            )
-            cfg.BaseConverter.merge(cfg.BaseNbConvertApp)
-            del cfg.BaseNbConvertApp
-
         super(NbGrader, self)._load_config(cfg, **kwargs)
         if self.coursedir:
             self.coursedir._load_config(cfg)
diff --git a/nbgrader/apps/nbgraderapp.py b/nbgrader/apps/nbgraderapp.py
index 23e84b3e..c5c22f8c 100755
--- a/nbgrader/apps/nbgraderapp.py
+++ b/nbgrader/apps/nbgraderapp.py
@@ -15,7 +15,6 @@ from .. import preprocessors
 from .. import plugins
 from ..coursedir import CourseDirectory
 from .. import exchange
-from .. import converters
 from .baseapp import nbgrader_aliases, nbgrader_flags
 from . import (
     NbGrader,
@@ -267,12 +266,6 @@ class NbGraderApp(NbGrader):
             if hasattr(ex, "class_traits") and ex.class_traits(config=True):
                 classes.append(ex)
 
-        # include all the converters
-        for ex_name in converters.__all__:
-            ex = getattr(converters, ex_name)
-            if hasattr(ex, "class_traits") and ex.class_traits(config=True):
-                classes.append(ex)
-
         return classes
 
     @catch_config_error
diff --git a/nbgrader/exchange/release.py b/nbgrader/exchange/release.py
index 6d1c89ca..3760d84a 100644
--- a/nbgrader/exchange/release.py
+++ b/nbgrader/exchange/release.py
@@ -4,7 +4,7 @@ from stat import (
     S_IRUSR, S_IWUSR, S_IXUSR,
     S_IRGRP, S_IWGRP, S_IXGRP,
     S_IROTH, S_IWOTH, S_IXOTH,
-    S_ISGID
+    S_ISGID, ST_MODE
 )
 
 from traitlets import Bool
@@ -17,6 +17,30 @@ class ExchangeRelease(Exchange):
 
     force = Bool(False, help="Force overwrite existing files in the exchange.").tag(config=True)
 
+    def ensure_root(self):
+        perms = S_IRUSR|S_IWUSR|S_IXUSR|S_IRGRP|S_IWGRP|S_IXGRP|S_IROTH|S_IWOTH|S_IXOTH
+
+        # if root doesn't exist, create it and set permissions
+        if not os.path.exists(self.root):
+            self.log.warning("Creating exchange directory: {}".format(self.root))
+            try:
+                os.makedirs(self.root)
+                os.chmod(self.root, perms)
+            except PermissionError:
+                self.fail("Could not create {}, permission denied.".format(self.root))
+
+        else:
+            old_perms = oct(os.stat(self.root)[ST_MODE] & 0o777)
+            new_perms = oct(perms & 0o777)
+            if old_perms != new_perms:
+                self.log.warning(
+                    "Permissions for exchange directory ({}) are invalid, changing them from {} to {}".format(
+                        self.root, old_perms, new_perms))
+                try:
+                    os.chmod(self.root, perms)
+                except PermissionError:
+                    self.fail("Could not change permissions of {}, permission denied.".format(self.root))
+
     def init_src(self):
         self.src_path = self.coursedir.format_path(self.coursedir.release_directory, '.', self.coursedir.assignment_id)
         if not os.path.isdir(self.src_path):

Make it clearer how to set permissions for the exchange directory
If the exchange directory hasn't been created when `nbgrader release` is run for the first time, an error occurs:

```
$ nbgrader release --Exchange.root=/tmp/exchange ps1
[ReleaseApp | WARNING] No nbgrader_config.py file found (rerun with --debug to see where nbgrader is looking)
[ReleaseApp | CRITICAL] Unwritable directory, please contact your instructor: /tmp/exchange
[ReleaseApp | ERROR] nbgrader release failed
```

This is confusing and not helpful for instructors. Instead, if the exchange directory doesn't exist, `nbgrader release` should create the directory for instructors and set it to have the correct permissions.
diff --git a/nbgrader/tests/apps/test_nbgrader_release.py b/nbgrader/tests/apps/test_nbgrader_release.py
index 93db81cb..0d8bf2dc 100644
--- a/nbgrader/tests/apps/test_nbgrader_release.py
+++ b/nbgrader/tests/apps/test_nbgrader_release.py
@@ -1,4 +1,6 @@
 import os
+import shutil
+import stat
 from os.path import join
 
 from .. import run_nbgrader
@@ -55,3 +57,16 @@ class TestNbGraderRelease(BaseTestApp):
         self._copy_file(join("files", "test.ipynb"), join(course_dir, "release", "ps1", "p1.ipynb"))
         self._release("--assignment=ps1", exchange)
         assert os.path.isfile(join(exchange, "abc101", "outbound", "ps1", "p1.ipynb"))
+
+    def test_no_exchange(self, exchange, course_dir):
+        shutil.rmtree(exchange)
+        self._copy_file(join("files", "test.ipynb"), join(course_dir, "release", "ps1", "p1.ipynb"))
+        self._release("--assignment=ps1", exchange)
+        assert os.path.isfile(join(exchange, "abc101", "outbound", "ps1", "p1.ipynb"))
+
+    def test_exchange_bad_perms(self, exchange, course_dir):
+        perms = stat.S_IRUSR|stat.S_IWUSR|stat.S_IXUSR|stat.S_IRGRP
+        os.chmod(exchange, perms)
+        self._copy_file(join("files", "test.ipynb"), join(course_dir, "release", "ps1", "p1.ipynb"))
+        self._release("--assignment=ps1", exchange)
+        assert os.path.isfile(join(exchange, "abc101", "outbound", "ps1", "p1.ipynb"))

pip install -r dev-requirements.txt -e .
parse_log_pytest
requirements.txt
pytest pytest-cov pytest-rerunfailures coverage selenium invoke sphinx codecov cov-core nbval
pip install -U pip wheel setuptools
3.5
dev-requirements.txt dev-requirements-windows.txt
pytest --no-header -rA --tb=line --color=no -p no:cacheprovider -W ignore::DeprecationWarning
alabaster==0.7.13
alembic==1.7.7
anyio==3.6.2
argon2-cffi==21.3.0
argon2-cffi-bindings==21.2.0
async-generator==1.10
attrs==22.2.0
Babel==2.11.0
backcall==0.2.0
bleach==4.1.0
certifi==2021.5.30
cffi==1.15.1
charset-normalizer==2.0.12
codecov==2.1.13
comm==0.1.4
contextvars==2.4
cov-core==1.15.0
coverage==6.2
dataclasses==0.8
decorator==5.1.1
defusedxml==0.7.1
docutils==0.18.1
entrypoints==0.4
greenlet==2.0.2
idna==3.10
imagesize==1.4.1
immutables==0.19
importlib-metadata==4.8.3
importlib-resources==5.4.0
iniconfig==1.1.1
invoke==2.2.0
ipykernel==5.5.6
ipython==7.16.3
ipython-genutils==0.2.0
ipywidgets==7.8.5
jedi==0.17.2
Jinja2==3.0.3
json5==0.9.16
jsonschema==3.2.0
jupyter==1.1.1
jupyter-client==7.1.2
jupyter-console==6.4.3
jupyter-core==4.9.2
jupyter-server==1.13.1
jupyterlab==3.2.9
jupyterlab-pygments==0.1.2
jupyterlab-server==2.10.3
jupyterlab_widgets==1.1.11
Mako==1.1.6
MarkupSafe==2.0.1
mistune==0.8.4
nbclassic==0.3.5
nbclient==0.5.9
nbconvert==6.0.7
nbformat==5.1.3
-e git+https://github.com/jupyter/nbgrader.git@7b9b431e873d1b787f269373140f0de31636b06c#egg=nbgrader
nbval==0.10.0
nest-asyncio==1.6.0
notebook==6.4.10
packaging==21.3
pandocfilters==1.5.1
parso==0.7.1
pexpect==4.9.0
pickleshare==0.7.5
pluggy==1.0.0
prometheus-client==0.17.1
prompt-toolkit==3.0.36
ptyprocess==0.7.0
py==1.11.0
pycparser==2.21
pyenchant==3.2.2
Pygments==2.14.0
pyparsing==3.1.4
pyrsistent==0.18.0
pytest==7.0.1
pytest-cov==4.0.0
pytest-rerunfailures==10.3
python-dateutil==2.9.0.post0
pytz==2025.2
pyzmq==25.1.2
requests==2.27.1
selenium==3.141.0
Send2Trash==1.8.3
six==1.17.0
sniffio==1.2.0
snowballstemmer==2.2.0
Sphinx==5.3.0
sphinx-rtd-theme==2.0.0
sphinxcontrib-applehelp==1.0.2
sphinxcontrib-devhelp==1.0.2
sphinxcontrib-htmlhelp==2.0.0
sphinxcontrib-jquery==4.1
sphinxcontrib-jsmath==1.0.1
sphinxcontrib-qthelp==1.0.3
sphinxcontrib-serializinghtml==1.1.5
sphinxcontrib-spelling==7.7.0
SQLAlchemy==1.4.54
terminado==0.12.1
testpath==0.6.0
tomli==1.2.3
tornado==6.1
traitlets==4.3.3
typing_extensions==4.1.1
urllib3==1.26.20
wcwidth==0.2.13
webencodings==0.5.1
websocket-client==1.3.1
widgetsnbextension==3.6.10
zipp==3.6.0

name: nbgrader
channels:
  - defaults
  - https://repo.anaconda.com/pkgs/main
  - https://repo.anaconda.com/pkgs/r
  - conda-forge
dependencies:
  - _libgcc_mutex=0.1=main
  - _openmp_mutex=5.1=1_gnu
  - ca-certificates=2025.2.25=h06a4308_0
  - certifi=2021.5.30=py36h06a4308_0
  - ld_impl_linux-64=2.40=h12ee557_0
  - libffi=3.3=he6710b0_2
  - libgcc-ng=11.2.0=h1234567_1
  - libgomp=11.2.0=h1234567_1
  - libstdcxx-ng=11.2.0=h1234567_1
  - ncurses=6.4=h6a678d5_0
  - openssl=1.1.1w=h7f8727e_0
  - python=3.6.13=h12debd9_1
  - readline=8.2=h5eee18b_0
  - sqlite=3.45.3=h5eee18b_0
  - tk=8.6.14=h39e8969_0
  - wheel=0.37.1=pyhd3eb1b0_0
  - xz=5.6.4=h5eee18b_1
  - zlib=1.2.13=h5eee18b_1
  - pip:
      - alabaster==0.7.13
      - alembic==1.7.7
      - anyio==3.6.2
      - argon2-cffi==21.3.0
      - argon2-cffi-bindings==21.2.0
      - async-generator==1.10
      - attrs==22.2.0
      - babel==2.11.0
      - backcall==0.2.0
      - bleach==4.1.0
      - cffi==1.15.1
      - charset-normalizer==2.0.12
      - codecov==2.1.13
      - comm==0.1.4
      - contextvars==2.4
      - cov-core==1.15.0
      - coverage==6.2
      - dataclasses==0.8
      - decorator==5.1.1
      - defusedxml==0.7.1
      - docutils==0.18.1
      - entrypoints==0.4
      - greenlet==2.0.2
      - idna==3.10
      - imagesize==1.4.1
      - immutables==0.19
      - importlib-metadata==4.8.3
      - importlib-resources==5.4.0
      - iniconfig==1.1.1
      - invoke==2.2.0
      - ipykernel==5.5.6
      - ipython==7.16.3
      - ipython-genutils==0.2.0
      - ipywidgets==7.8.5
      - jedi==0.17.2
      - jinja2==3.0.3
      - json5==0.9.16
      - jsonschema==3.2.0
      - jupyter==1.1.1
      - jupyter-client==7.1.2
      - jupyter-console==6.4.3
      - jupyter-core==4.9.2
      - jupyter-server==1.13.1
      - jupyterlab==3.2.9
      - jupyterlab-pygments==0.1.2
      - jupyterlab-server==2.10.3
      - jupyterlab-widgets==1.1.11
      - mako==1.1.6
      - markupsafe==2.0.1
      - mistune==0.8.4
      - nbclassic==0.3.5
      - nbclient==0.5.9
      - nbconvert==6.0.7
      - nbformat==5.1.3
      - nbval==0.10.0
      - nest-asyncio==1.6.0
      - notebook==6.4.10
      - packaging==21.3
      - pandocfilters==1.5.1
      - parso==0.7.1
      - pexpect==4.9.0
      - pickleshare==0.7.5
      - pip==21.3.1
      - pluggy==1.0.0
      - prometheus-client==0.17.1
      - prompt-toolkit==3.0.36
      - ptyprocess==0.7.0
      - py==1.11.0
      - pycparser==2.21
      - pyenchant==3.2.2
      - pygments==2.14.0
      - pyparsing==3.1.4
      - pyrsistent==0.18.0
      - pytest==7.0.1
      - pytest-cov==4.0.0
      - pytest-rerunfailures==10.3
      - python-dateutil==2.9.0.post0
      - pytz==2025.2
      - pyzmq==25.1.2
      - requests==2.27.1
      - selenium==3.141.0
      - send2trash==1.8.3
      - setuptools==59.6.0
      - six==1.17.0
      - sniffio==1.2.0
      - snowballstemmer==2.2.0
      - sphinx==5.3.0
      - sphinx-rtd-theme==2.0.0
      - sphinxcontrib-applehelp==1.0.2
      - sphinxcontrib-devhelp==1.0.2
      - sphinxcontrib-htmlhelp==2.0.0
      - sphinxcontrib-jquery==4.1
      - sphinxcontrib-jsmath==1.0.1
      - sphinxcontrib-qthelp==1.0.3
      - sphinxcontrib-serializinghtml==1.1.5
      - sphinxcontrib-spelling==7.7.0
      - sqlalchemy==1.4.54
      - terminado==0.12.1
      - testpath==0.6.0
      - tomli==1.2.3
      - tornado==6.1
      - traitlets==4.3.3
      - typing-extensions==4.1.1
      - urllib3==1.26.20
      - wcwidth==0.2.13
      - webencodings==0.5.1
      - websocket-client==1.3.1
      - widgetsnbextension==3.6.10
      - zipp==3.6.0
prefix: /opt/conda/envs/nbgrader

nbgrader/tests/apps/test_nbgrader_release.py::TestNbGraderRelease::test_no_exchange
nbgrader/tests/apps/test_nbgrader_release.py::TestNbGraderRelease::test_help nbgrader/tests/apps/test_nbgrader_release.py::TestNbGraderRelease::test_no_course_id nbgrader/tests/apps/test_nbgrader_release.py::TestNbGraderRelease::test_release nbgrader/tests/apps/test_nbgrader_release.py::TestNbGraderRelease::test_force_release nbgrader/tests/apps/test_nbgrader_release.py::TestNbGraderRelease::test_release_with_assignment_flag nbgrader/tests/apps/test_nbgrader_release.py::TestNbGraderRelease::test_exchange_bad_perms
nbgrader/apps/nbgraderapp.py nbgrader/apps/baseapp.py nbgrader/exchange/release.py
nbgrader/apps/nbgraderapp.py nbgrader/apps/baseapp.py nbgrader/exchange/release.py