bug: sent_tokenize with engine="whitespace" should return [] not [[]]

[bact]

Description

sent_tokenize(str, engine="whitespace") returns a list of a list of string, instead of a list of string.

Expected results

sent_tokenize should return a list ([]), not a list of a list ([[]])

Current results

https://github.com/PyThaiNLP/pythainlp/actions/runs/11627805664/job/32381817268

======================================================================
FAIL: test_sent_tokenize (tests.test_tokenize.TokenizeTestCase)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/runner/work/pythainlp/pythainlp/tests/test_tokenize.py", line 222, in test_sent_tokenize
    self.assertEqual(
AssertionError: Lists differ: [['รักน้ำ', 'รักปลา', '']] != ['รักน้ำ', 'รักปลา', '']

First differing element 0:
['รักน้ำ', 'รักปลา', '']
'รักน้ำ'

Second list contains 2 additional elements.
First extra element 1:
'รักปลา'

- [['รักน้ำ', 'รักปลา', '']]
? -                        -

+ ['รักน้ำ', 'รักปลา', '']

Steps to reproduce

        self.assertEqual(
            sent_tokenize("รักน้ำ  รักปลา  ", engine="whitespace"),
            ["รักน้ำ", "รักปลา", ""],
        )

PyThaiNLP version

5.0.4

Python version

All

Operating system and version

All

More info

No response

Possible solution

No response

Files

No response