diff --git a/bumpversion/cli.py b/bumpversion/cli.py
index 7b9cc86e..bcb08d26 100644
--- a/bumpversion/cli.py
+++ b/bumpversion/cli.py
@@ -141,7 +141,7 @@ def cli(ctx: Context) -> None:
 )
 @click.option(
     "--regex/--no-regex",
-    default=False,
+    default=None,
     envvar="BUMPVERSION_REGEX",
     help="Treat the search parameter as a regular expression or explicitly do not treat it as a regular expression.",
 )
@@ -232,7 +232,7 @@ def bump(
     serialize: Optional[List[str]],
     search: Optional[str],
     replace: Optional[str],
-    regex: bool,
+    regex: Optional[bool],
     no_configured_files: bool,
     ignore_missing_version: bool,
     dry_run: bool,
diff --git a/bumpversion/files.py b/bumpversion/files.py
index efccdd3a..a5f8c1e1 100644
--- a/bumpversion/files.py
+++ b/bumpversion/files.py
@@ -1,4 +1,5 @@
 """Methods for changing files."""
+import os.path
 import re
 from copy import deepcopy
 from difflib import context_diff
@@ -94,7 +95,18 @@ def __init__(
         self._newlines: Optional[str] = None
 
     def get_file_contents(self) -> str:
-        """Return the contents of the file."""
+        """
+        Return the contents of the file.
+
+        Raises:
+            FileNotFoundError: if the file doesn't exist
+
+        Returns:
+            The contents of the file
+        """
+        if not os.path.exists(self.file_change.filename):
+            raise FileNotFoundError(f"File not found: '{self.file_change.filename}'")
+
         with open(self.file_change.filename, "rt", encoding="utf-8") as f:
             contents = f.read()
             self._newlines = f.newlines[0] if isinstance(f.newlines, tuple) else f.newlines
diff --git a/bumpversion/version_part.py b/bumpversion/version_part.py
index 6058fd59..13430d35 100644
--- a/bumpversion/version_part.py
+++ b/bumpversion/version_part.py
@@ -150,6 +150,18 @@ def __init__(
         self.search = search
         self.replace = replace
 
+    def __repr__(self) -> str:
+        return f"<bumpversion.VersionConfig:{self.parse_regex.pattern}:{self.serialize_formats}>"
+
+    def __eq__(self, other: Any) -> bool:
+        return (
+            self.parse_regex.pattern == other.parse_regex.pattern
+            and self.serialize_formats == other.serialize_formats
+            and self.part_configs == other.part_configs
+            and self.search == other.search
+            and self.replace == other.replace
+        )
+
     @property
     def order(self) -> List[str]:
         """
diff --git a/tests/fixtures/basic_cfg.toml b/tests/fixtures/basic_cfg.toml
index a1b14936..7808ae95 100644
--- a/tests/fixtures/basic_cfg.toml
+++ b/tests/fixtures/basic_cfg.toml
@@ -41,6 +41,6 @@ replace = """**unreleased**
 [tool.bumpversion.parts.release]
 optional_value = "gamma"
 values =[
-	"dev",
-	"gamma",
+    "dev",
+    "gamma",
 ]
diff --git a/tests/fixtures/regex_test_config.toml b/tests/fixtures/regex_test_config.toml
new file mode 100644
index 00000000..46eeca1a
--- /dev/null
+++ b/tests/fixtures/regex_test_config.toml
@@ -0,0 +1,8 @@
+[tool.bumpversion]
+current_version = "4.7.1"
+regex = true
+
+[[tool.bumpversion.files]]
+filename = "./citation.cff"
+search = "date-released: \\d{{4}}-\\d{{2}}-\\d{{2}}"
+replace = "date-released: {utcnow:%Y-%m-%d}"
diff --git a/tests/test_cli.py b/tests/test_cli.py
index 14314cac..638d7df4 100644
--- a/tests/test_cli.py
+++ b/tests/test_cli.py
@@ -2,6 +2,7 @@
 import shutil
 import subprocess
 import traceback
+from datetime import datetime
 from pathlib import Path
 
 import pytest
@@ -45,6 +46,32 @@ def test_bump_no_configured_files(mocker, tmp_path):
     assert len(call_args[2].files) == 0
 
 
+def test_bump_nested_regex(tmp_path: Path, fixtures_path: Path, caplog):
+    """
+    Arrange/Act: Run the `bump` subcommand with --no-configured-files.
+
+    Assert: There is no configured files specified to modify
+    """
+    cff_path = tmp_path / "citation.cff"
+    cff_path.write_text("cff-version: 1.2.0\ndate-released: 2023-09-19\n")
+    content = fixtures_path.joinpath("regex_test_config.toml").read_text()
+    config_path = tmp_path / ".bumpversion.toml"
+    config_path.write_text(content)
+
+    runner: CliRunner = CliRunner()
+    with inside_dir(tmp_path):
+        result: Result = runner.invoke(cli.cli, ["bump", "-vv", "patch"])
+
+    if result.exit_code != 0:
+        print(result.output)
+        print(caplog.text)
+
+    assert result.exit_code == 0
+
+    now = datetime.now().isoformat()[:10]
+    assert cff_path.read_text() == f"cff-version: 1.2.0\ndate-released: {now}\n"
+
+
 def test_bump_legacy(mocker, tmp_path):
     """
     Arrange/Act: Run the `bump` subcommand with --no-configured-files.