fix: from_json() preserves falsy data instead of collapsing to None

HISTORY

@@ -1,5 +1,8 @@
 # History
 
+Jul 25, 2026
+from_json() no longer collapses falsy data values (0, False, "") to None.
+
 Mar 27, 2023 V1.6.3
 Apply to black code style. Migrate future to six
 

tests/test_tree_io.py

@@ -162,6 +162,28 @@ def test_to_json_without_data(self):
         project_data = parsed["Project"]
         self.assertNotIn("data", project_data)
 
+    def test_from_json_preserves_falsy_data(self):
+        """from_json must preserve falsy-but-valid data values, not collapse them to None."""
+        # assertIs on the type is deliberate: assertEqual alone would accept
+        # False for 0 and 0 for 0.0, which would hide a type change.
+        for value in [0, 0.0, False, "", [], {}]:
+            with self.subTest(data=value):
+                tree = Tree()
+                tree.create_node("root", "root", data=value)
+                restored = Tree.from_json(tree.to_json(with_data=True))
+                data = restored.all_nodes()[0].data
+                self.assertEqual(data, value)
+                self.assertIs(type(data), type(value))
+
+    def test_from_json_preserves_none_and_truthy_data(self):
+        """None data stays None, and truthy data is unaffected by the falsy fix."""
+        for value in [None, 42, "text", ["a"], {"k": "v"}]:
+            with self.subTest(data=value):
+                tree = Tree()
+                tree.create_node("root", "root", data=value)
+                restored = Tree.from_json(tree.to_json(with_data=True))
+                self.assertEqual(restored.all_nodes()[0].data, value)
+
     def test_from_map_basic(self):
         """Test from_map basic functionality."""
         child_parent_dict = {"CEO": None, "CTO": "CEO", "CFO": "CEO", "VP_Eng": "CTO", "Developer": "VP_Eng"}

treelib/tree.py

@@ -248,7 +248,7 @@ def from_json(cls, raw: Union[str, bytes, bytearray]):
         def _append_node(subtree, parent_id=None):
             for tag, node_info in subtree.items():
                 node_id = node_info.get("id") or None
-                node_data = node_info.get("data") or None
+                node_data = node_info.get("data")
 
                 node = tree.create_node(tag=tag, identifier=node_id, parent=parent_id, data=node_data)