diff --git a/src/gdiffer/parser.py b/src/gdiffer/parser.py
index 39071ab..b230ba9 100644
--- a/src/gdiffer/parser.py
+++ b/src/gdiffer/parser.py
@@ -1,7 +1,6 @@
 """Diff parser for unified git diff format."""
 
 import re
-from typing import Optional
 
 from gdiffer.models import DiffFile, DiffHunk
 
@@ -16,6 +15,7 @@ class DiffParser:
         self.errors: list[str] = []
 
     def parse(self, diff_content: str) -> list[DiffFile]:
+        """Parse diff content and return list of DiffFile objects."""
         self.files = []
         self.errors = []
 
@@ -42,7 +42,7 @@ class DiffParser:
 
             i += 1
 
-    def _parse_file(self, lines: list[str], start: int) -> Optional[DiffFile]:
+    def _parse_file(self, lines: list[str], start: int) -> DiffFile | None:
         if start >= len(lines):
             return None
 
@@ -120,7 +120,7 @@ class DiffParser:
 
         return file_obj
 
-    def _parse_hunk(self, lines: list[str], start: int) -> tuple[Optional[DiffHunk], int]:
+    def _parse_hunk(self, lines: list[str], start: int) -> tuple[DiffHunk | None, int]:
         if start >= len(lines):
             return None, 0
 
@@ -198,6 +198,6 @@ def parse_diff(diff_content: str) -> list[DiffFile]:
 
 def parse_diff_from_file(filepath: str) -> list[DiffFile]:
     """Read a diff file and parse its contents."""
-    with open(filepath, 'r') as f:
+    with open(filepath) as f:
         content = f.read()
     return parse_diff(content)