@@ -831,7 +831,7 @@ def execute(self,
         except cmd_not_found_exception as err:
             raise GitCommandNotFound(redacted_command, err) from err
         else:
-            proc = cast(Popen, proc)
+            # replace with a typeguard for Popen[bytes]?
             proc.stdout = cast(BinaryIO, proc.stdout)
             proc.stderr = cast(BinaryIO, proc.stderr)
 
 
@@ -34,7 +34,7 @@
 from typing import (Any, Callable, IO, List, Dict, Sequence,
                     TYPE_CHECKING, Tuple, Union, cast, overload)
 
-from git.types import Lit_config_levels, ConfigLevels_Tup, PathLike, TBD, assert_never
+from git.types import Lit_config_levels, ConfigLevels_Tup, PathLike, TBD, assert_never, is_config_level
 
 if TYPE_CHECKING:
     from git.repo.base import Repo
@@ -54,6 +54,7 @@
 
 CONFIG_LEVELS: ConfigLevels_Tup = ("system", "user", "global", "repository")
 
+
 # Section pattern to detect conditional includes.
 # https://git-scm.com/docs/git-config#_conditional_includes
 CONDITIONAL_INCLUDE_REGEXP = re.compile(r"(?<=includeIf )\"(gitdir|gitdir/i|onbranch):(.+)\"")
@@ -310,7 +311,7 @@ def __init__(self, file_or_files: Union[None, PathLike, 'BytesIO', Sequence[Unio
                 if read_only:
                     self._file_or_files = [get_config_path(f)
                                            for f in CONFIG_LEVELS
-                                           if f != 'repository']
+                                           if is_config_level(f) and f != 'repository']
                 else:
                     raise ValueError("No configuration level or configuration files specified")
             else:
 
@@ -113,7 +113,7 @@ class IndexFile(LazyMixin, diff.Diffable, Serializable):
     _VERSION = 2            # latest version we support
     S_IFGITLINK = S_IFGITLINK  # a submodule
 
-    def __init__(self, repo: 'Repo', file_path: PathLike = None) -> None:
+    def __init__(self, repo: 'Repo', file_path: Union[PathLike, None] = None) -> None:
         """Initialize this Index instance, optionally from the given ``file_path``.
         If no file_path is given, we will be created from the current index file.
 
@@ -665,7 +665,7 @@ def _entries_for_paths(self, paths: List[str], path_rewriter: Callable, fprogres
         return entries_added
 
     def add(self, items: Sequence[Union[PathLike, Blob, BaseIndexEntry, 'Submodule']], force: bool = True,
-            fprogress: Callable = lambda *args: None, path_rewriter: Callable = None,
+            fprogress: Callable = lambda *args: None, path_rewriter: Union[Callable[..., PathLike], None] = None,
             write: bool = True, write_extension_data: bool = False) -> List[BaseIndexEntry]:
         """Add files from the working tree, specific blobs or BaseIndexEntries
         to the index.
@@ -970,7 +970,8 @@ def move(self, items: Sequence[Union[PathLike, Blob, BaseIndexEntry, 'Submodule'
         return out
 
     def commit(self, message: str, parent_commits=None, head: bool = True, author: Union[None, 'Actor'] = None,
-               committer: Union[None, 'Actor'] = None, author_date: str = None, commit_date: str = None,
+               committer: Union[None, 'Actor'] = None, author_date: Union[str, None] = None,
+               commit_date: Union[str, None] = None,
                skip_hooks: bool = False) -> Commit:
         """Commit the current default index file, creating a commit object.
         For more information on the arguments, see tree.commit.
@@ -1265,7 +1266,8 @@ def reset(self, commit: Union[Commit, 'Reference', str] = 'HEAD', working_tree:
 
     @ default_index
     def diff(self, other: Union[diff.Diffable.Index, 'IndexFile.Index', Treeish, None, object] = diff.Diffable.Index,
-             paths: Union[str, List[PathLike], Tuple[PathLike, ...]] = None, create_patch: bool = False, **kwargs: Any
+             paths: Union[str, List[PathLike], Tuple[PathLike, ...], None] = None,
+             create_patch: bool = False, **kwargs: Any
              ) -> diff.DiffIndex:
         """Diff this index against the working copy or a Tree or Commit object
 
 
@@ -80,7 +80,7 @@ class Commit(base.Object, TraversableIterableObj, Diffable, Serializable):
                  "message", "parents", "encoding", "gpgsig")
     _id_attribute_ = "hexsha"
 
-    def __init__(self, repo: 'Repo', binsha: bytes, tree: 'Tree' = None,
+    def __init__(self, repo: 'Repo', binsha: bytes, tree: Union['Tree', None] = None,
                  author: Union[Actor, None] = None,
                  authored_date: Union[int, None] = None,
                  author_tz_offset: Union[None, float] = None,
 
@@ -115,7 +115,7 @@ def __init__(self, repo: 'Repo', binsha: bytes,
                  path: Union[PathLike, None] = None,
                  name: Union[str, None] = None,
                  parent_commit: Union[Commit_ish, None] = None,
-                 url: str = None,
+                 url: Union[str, None] = None,
                  branch_path: Union[PathLike, None] = None
                  ) -> None:
         """Initialize this instance with its attributes. We only document the ones
@@ -339,7 +339,7 @@ def _write_git_file_and_module_config(cls, working_tree_dir: PathLike, module_ab
     @classmethod
     def add(cls, repo: 'Repo', name: str, path: PathLike, url: Union[str, None] = None,
             branch: Union[str, None] = None, no_checkout: bool = False, depth: Union[int, None] = None,
-            env: Mapping[str, str] = None, clone_multi_options: Union[Sequence[TBD], None] = None
+            env: Union[Mapping[str, str], None] = None, clone_multi_options: Union[Sequence[TBD], None] = None
             ) -> 'Submodule':
         """Add a new submodule to the given repository. This will alter the index
         as well as the .gitmodules file, but will not create a new commit.
@@ -481,7 +481,7 @@ def add(cls, repo: 'Repo', name: str, path: PathLike, url: Union[str, None] = No
 
     def update(self, recursive: bool = False, init: bool = True, to_latest_revision: bool = False,
                progress: Union['UpdateProgress', None] = None, dry_run: bool = False,
-               force: bool = False, keep_going: bool = False, env: Mapping[str, str] = None,
+               force: bool = False, keep_going: bool = False, env: Union[Mapping[str, str], None] = None,
                clone_multi_options: Union[Sequence[TBD], None] = None):
         """Update the repository of this submodule to point to the checkout
         we point at with the binsha of this instance.
 
@@ -216,7 +216,6 @@ def __init__(self, repo: 'Repo', binsha: bytes, mode: int = tree_id << 12, path:
     def _get_intermediate_items(cls, index_object: 'Tree',
                                 ) -> Union[Tuple['Tree', ...], Tuple[()]]:
         if index_object.type == "tree":
-            index_object = cast('Tree', index_object)
             return tuple(index_object._iter_convert_to_object(index_object._cache))
         return ()
 
 
@@ -36,7 +36,7 @@
 
 # typing ------------------------------------------------------
 
-from git.types import TBD, PathLike, Lit_config_levels, Commit_ish, Tree_ish
+from git.types import TBD, PathLike, Lit_config_levels, Commit_ish, Tree_ish, is_config_level
 from typing import (Any, BinaryIO, Callable, Dict,
                     Iterator, List, Mapping, Optional, Sequence,
                     TextIO, Tuple, Type, Union,
@@ -498,7 +498,7 @@ def config_reader(self, config_level: Optional[Lit_config_levels] = None) -> Git
             unknown, instead the global path will be used."""
         files = None
         if config_level is None:
-            files = [self._get_config_path(f) for f in self.config_level]
+            files = [self._get_config_path(f) for f in self.config_level if is_config_level(f)]
         else:
             files = [self._get_config_path(config_level)]
         return GitConfigParser(files, read_only=True, repo=self)
@@ -623,7 +623,7 @@ def is_ancestor(self, ancestor_rev: 'Commit', rev: 'Commit') -> bool:
             raise
         return True
 
-    def is_valid_object(self, sha: str, object_type: str = None) -> bool:
+    def is_valid_object(self, sha: str, object_type: Union[str, None] = None) -> bool:
         try:
             complete_sha = self.odb.partial_to_complete_sha_hex(sha)
             object_info = self.odb.info(complete_sha)
@@ -976,7 +976,7 @@ def blame(self, rev: TBD, file: TBD, incremental: bool = False, **kwargs: Any
         return blames
 
     @classmethod
-    def init(cls, path: PathLike = None, mkdir: bool = True, odbt: Type[GitCmdObjectDB] = GitCmdObjectDB,
+    def init(cls, path: Union[PathLike, None] = None, mkdir: bool = True, odbt: Type[GitCmdObjectDB] = GitCmdObjectDB,
              expand_vars: bool = True, **kwargs: Any) -> 'Repo':
         """Initialize a git repository at the given path if specified
 
 
@@ -39,20 +39,11 @@
 
 
 def is_config_level(inp: str) -> TypeGuard[Lit_config_levels]:
-    return inp in ('system', 'global', 'user', 'repository')
+    # return inp in get_args(Lit_config_level)  # only py >= 3.8
+    return inp in ("system", "user", "global", "repository")
 
 
-class ConfigLevels_NT(NamedTuple):
-    """NamedTuple of allowed CONFIG_LEVELS"""
-    # works for pylance, but not mypy
-    system: Literal['system']
-    user: Literal['user']
-    global_: Literal['global']
-    repository: Literal['repository']
-
-
-ConfigLevels_Tup = Tuple[Lit_config_levels, Lit_config_levels, Lit_config_levels, Lit_config_levels]
-# Typing this as specific literals breaks for mypy
+ConfigLevels_Tup = Tuple[Literal['system'], Literal['user'], Literal['global'], Literal['repository']]
 
 
 def assert_never(inp: NoReturn, exc: Union[Exception, None] = None) -> NoReturn:
 
@@ -3,6 +3,11 @@
 
 # TODO: enable when we've fully annotated everything
 # disallow_untyped_defs = True
+no_implicit_optional = True
+warn_redundant_casts = True
+# warn_unused_ignores = True
+# warn_unreachable = True
+pretty = True
 
 # TODO: remove when 'gitdb' is fully annotated
 [mypy-gitdb.*]