text-splitters: Fix/recursive json splitter data persistence issue (#21529)

Thank you for contributing to LangChain!

**Description:** Noticed an issue with when I was calling
`RecursiveJsonSplitter().split_json()` multiple times that I was getting
weird results. I found an issue where `chunks` list in the `_json_split`
method. If chunks is not provided when _json_split (which is the case
when split_json calls _json_split) then the same list is used for
subsequent calls to `_json_split`.


You can see this in the test case i also added to this commit.

Output should be: 
```
[{'a': 1, 'b': 2}]
[{'c': 3, 'd': 4}]
```

Instead you get:
```
[{'a': 1, 'b': 2}]
[{'a': 1, 'b': 2, 'c': 3, 'd': 4}]
```

---------

Co-authored-by: Nuno Campos <nuno@langchain.dev>
Co-authored-by: isaac hershenson <ihershenson@hmc.edu>
Co-authored-by: Isaac Francisco <78627776+isahers1@users.noreply.github.com>

libs/text-splitters/langchain_text_splitters/json.py

@@ -55,7 +55,7 @@ class RecursiveJsonSplitter:
         Split json into maximum size dictionaries while preserving structure.
         """
         current_path = current_path or []
-        chunks = chunks or [{}]
+        chunks = chunks if chunks is not None else [{}]
         if isinstance(data, dict):
             for key, value in data.items():
                 new_path = current_path + [key]

libs/text-splitters/tests/unit_tests/test_text_splitters.py

@@ -1953,3 +1953,24 @@ def test_split_json_with_lists() -> None:
     texts_list = splitter.split_text(json_data=test_data_list, convert_lists=True)
 
     assert len(texts_list) >= len(texts)
+
+
+def test_split_json_many_calls() -> None:
+    x = {"a": 1, "b": 2}
+    y = {"c": 3, "d": 4}
+
+    splitter = RecursiveJsonSplitter()
+    chunk0 = splitter.split_json(x)
+    assert chunk0 == [{"a": 1, "b": 2}]
+
+    chunk1 = splitter.split_json(y)
+    assert chunk1 == [{"c": 3, "d": 4}]
+
+    # chunk0 is now altered by creating chunk1
+    assert chunk0 == [{"a": 1, "b": 2}]
+
+    chunk0_output = [{"a": 1, "b": 2}]
+    chunk1_output = [{"c": 3, "d": 4}]
+
+    assert chunk0 == chunk0_output
+    assert chunk1 == chunk1_output