Fix: pipeline debug... (#10206)

### What problem does this PR solve?

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)
- [x] New Feature (non-breaking change which adds functionality)

rag/nlp/__init__.py

@@ -522,7 +522,9 @@ def naive_merge(sections: str | list, chunk_token_num=128, delimiter="\n。；
     from deepdoc.parser.pdf_parser import RAGFlowPdfParser
     if not sections:
         return []
-    if isinstance(sections[0], type("")):
+    if isinstance(sections, str):
+        sections = [sections]
+    if isinstance(sections[0], str):
         sections = [(s, "") for s in sections]
     cks = [""]
     tk_nums = [0]