fix: do not interpret None in config files

This commit addresses
[this comment (pawamoy#55)](pawamoy#55 (comment)).

Please note that this will disallow unsetting options if a hierarchy of
config files were to be implemented at some point.

docs/usage.md

@@ -450,7 +450,6 @@ output = 'output.log'
 parse-refs = false
 parse-trailers = false
 repository = '.'
-sections = 'none'
 template = 'angular'
 version-regex = '^## \[(?P<version>v?[^\]]+)'
 ```

src/git_changelog/cli.py

@@ -338,7 +338,7 @@ def read_config(
                 or new_settings.get("tool.git-changelog", {})
             )
 
-            if not new_settings:  # Likely, pyproject.toml did not have a git-changelog section
+            if not new_settings:  # pyproject.toml did not have a git-changelog section
                 continue
 
         # Settings can have hyphens like in the CLI
@@ -348,14 +348,18 @@ def read_config(
 
         # Massage found values to meet expectations
         # Parse sections
-        if "sections" in new_settings and new_settings["sections"] is not None:
-            sections = new_settings["sections"]
+        if "sections" in new_settings:
+            # Remove "sections" from dict, only restore if the list is valid
+            sections = new_settings.pop("sections", None)
             if isinstance(sections, str):
-                sections = [s.strip() for s in sections.split(",")]
+                sections = sections.split(",")
 
-            new_settings["sections"] = [
-                s.strip() for s in sections if s.strip() and s.strip() != "none"
-            ] or None
+            sections = [
+                s.strip() for s in sections if isinstance(s, str) and s.strip()
+            ]
+
+            if sections:  # toml doesn't store null/nil
+                new_settings["sections"] = sections
 
         project_config.update(new_settings)
         break

tests/test_cli.py

@@ -57,14 +57,16 @@ def test_passing_repository_and_sections(tmp_path: Path, args: tuple[str]) -> No
 @pytest.mark.parametrize("is_pyproject", [True, False, None])
 @pytest.mark.parametrize(("sections", "sections_value"), [
     (None, None),
-    ("none", None),
-    ("force-null", None),
     ("", None),
-    ("none, none, none", None),
+    (",,", None),
+    ("force-null", None),
     ("a, b, ", ["a", "b"]),
     ("a,  , ", ["a"]),
     ("a, b, c", ["a", "b", "c"]),
     (["a", "b", "c"], ["a", "b", "c"]),
+    # Uncomment if None/null is once allowed as a value
+    # ("none", None),
+    # ("none, none, none", None),
 ])
 @pytest.mark.parametrize("parse_refs", [None, False, True])
 def test_config_reading(