Apply suggestions from code review

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

Author: RyanRana

packages/moss-cli/src/moss_cli/documents.py

@@ -68,11 +68,26 @@ def _parse_jsonl_docs(raw: str, source: str = "input") -> List[DocumentInfo]:
 
 
 def _parse_csv_docs(content: str) -> List[DocumentInfo]:
-    reader = csv.DictReader(io.StringIO(content))
+reader = csv.DictReader(io.StringIO(content, newline=""))
     if reader.fieldnames is None:
         raise typer.BadParameter("CSV is empty: expected a header row")
 
     reader.fieldnames = [(name or "").strip() for name in reader.fieldnames]
+
+    seen = set()
+    dupes = set()
+    for name in reader.fieldnames:
+        if not name:
+            continue
+        if name in seen:
+            dupes.add(name)
+        else:
+            seen.add(name)
+    if dupes:
+        raise typer.BadParameter(
+            f"CSV header has duplicate column name(s): {', '.join(sorted(dupes))}"
+        )
+
     missing = [name for name in ("id", "text") if name not in reader.fieldnames]
     if missing:
         raise typer.BadParameter(
@@ -104,6 +119,9 @@ def _parse_csv_docs(content: str) -> List[DocumentInfo]:
 
 
 def _parse_csv_json(value: Optional[str], column: str, line_no: int) -> Any:
+    if value is None:
+        return None
+    value = value.strip()
     if not value:
         return None
     try: