fix: variable not found #26144 (#26155)

Signed-off-by: -LAN- <laipz8200@outlook.com>
Co-authored-by: lix43 <lix43@chinatelecom.cn>
Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
Co-authored-by: -LAN- <laipz8200@outlook.com>

api/core/workflow/entities/variable_pool.py

         """Extract the actual value from an ObjectSegment."""
         return obj.value if isinstance(obj, ObjectSegment) else obj
 
-    def _get_nested_attribute(self, obj: Mapping[str, Any], attr: str):
-        """Get a nested attribute from a dictionary-like object."""
-        if not isinstance(obj, dict):
+    def _get_nested_attribute(self, obj: Mapping[str, Any], attr: str) -> Segment | None:
+        """
+        Get a nested attribute from a dictionary-like object.
+
+        Args:
+            obj: The dictionary-like object to search.
+            attr: The key to look up.
+
+        Returns:
+            Segment | None:
+                The corresponding Segment built from the attribute value if the key exists,
+                otherwise None.
+        """
+        if not isinstance(obj, dict) or attr not in obj:
             return None
-        return obj.get(attr)
+        return variable_factory.build_segment(obj.get(attr))
 
     def remove(self, selector: Sequence[str], /):
         """

api/factories/variable_factory.py

     # below
     if value is None:
         return NoneSegment()
+    if isinstance(value, Segment):
+        return value
     if isinstance(value, str):
         return StringSegment(value=value)
     if isinstance(value, bool):

api/tests/unit_tests/core/workflow/entities/test_variable_pool.py

+from core.variables.segments import (
+    BooleanSegment,
+    IntegerSegment,
+    NoneSegment,
+    StringSegment,
+)
+from core.workflow.entities.variable_pool import VariablePool
+
+
+class TestVariablePoolGetAndNestedAttribute:
+    #
+    # _get_nested_attribute tests
+    #
+    def test__get_nested_attribute_existing_key(self):
+        pool = VariablePool.empty()
+        obj = {"a": 123}
+        segment = pool._get_nested_attribute(obj, "a")
+        assert segment is not None
+        assert segment.value == 123
+
+    def test__get_nested_attribute_missing_key(self):
+        pool = VariablePool.empty()
+        obj = {"a": 123}
+        segment = pool._get_nested_attribute(obj, "b")
+        assert segment is None
+
+    def test__get_nested_attribute_non_dict(self):
+        pool = VariablePool.empty()
+        obj = ["not", "a", "dict"]
+        segment = pool._get_nested_attribute(obj, "a")
+        assert segment is None
+
+    def test__get_nested_attribute_with_none_value(self):
+        pool = VariablePool.empty()
+        obj = {"a": None}
+        segment = pool._get_nested_attribute(obj, "a")
+        assert segment is not None
+        assert isinstance(segment, NoneSegment)
+
+    def test__get_nested_attribute_with_empty_string(self):
+        pool = VariablePool.empty()
+        obj = {"a": ""}
+        segment = pool._get_nested_attribute(obj, "a")
+        assert segment is not None
+        assert isinstance(segment, StringSegment)
+        assert segment.value == ""
+
+    #
+    # get tests
+    #
+    def test_get_simple_variable(self):
+        pool = VariablePool.empty()
+        pool.add(("node1", "var1"), "value1")
+        segment = pool.get(("node1", "var1"))
+        assert segment is not None
+        assert segment.value == "value1"
+
+    def test_get_missing_variable(self):
+        pool = VariablePool.empty()
+        result = pool.get(("node1", "unknown"))
+        assert result is None
+
+    def test_get_with_too_short_selector(self):
+        pool = VariablePool.empty()
+        result = pool.get(("only_node",))
+        assert result is None
+
+    def test_get_nested_object_attribute(self):
+        pool = VariablePool.empty()
+        obj_value = {"inner": "hello"}
+        pool.add(("node1", "obj"), obj_value)
+
+        # simulate selector with nested attr
+        segment = pool.get(("node1", "obj", "inner"))
+        assert segment is not None
+        assert segment.value == "hello"
+
+    def test_get_nested_object_missing_attribute(self):
+        pool = VariablePool.empty()
+        obj_value = {"inner": "hello"}
+        pool.add(("node1", "obj"), obj_value)
+
+        result = pool.get(("node1", "obj", "not_exist"))
+        assert result is None
+
+    def test_get_nested_object_attribute_with_falsy_values(self):
+        pool = VariablePool.empty()
+        obj_value = {
+            "inner_none": None,
+            "inner_empty": "",
+            "inner_zero": 0,
+            "inner_false": False,
+        }
+        pool.add(("node1", "obj"), obj_value)
+
+        segment_none = pool.get(("node1", "obj", "inner_none"))
+        assert segment_none is not None
+        assert isinstance(segment_none, NoneSegment)
+
+        segment_empty = pool.get(("node1", "obj", "inner_empty"))
+        assert segment_empty is not None
+        assert isinstance(segment_empty, StringSegment)
+        assert segment_empty.value == ""
+
+        segment_zero = pool.get(("node1", "obj", "inner_zero"))
+        assert segment_zero is not None
+        assert isinstance(segment_zero, IntegerSegment)
+        assert segment_zero.value == 0
+
+        segment_false = pool.get(("node1", "obj", "inner_false"))
+        assert segment_false is not None
+        assert isinstance(segment_false, BooleanSegment)
+        assert segment_false.value is False