diff --git a/python/packages/core/agent_framework/_types.py b/python/packages/core/agent_framework/_types.py
index 17dba475e3e..a21644a5789 100644
--- a/python/packages/core/agent_framework/_types.py
+++ b/python/packages/core/agent_framework/_types.py
@@ -1581,9 +1581,12 @@ def __add__(self, other: Content) -> Content:
 
     def _add_text_content(self, other: Content) -> Content:
         """Add two TextContent instances."""
+        self_text = self.text or ""
+        other_text = other.text or ""
+        combined_text = None if self.text is None and other.text is None else self_text + other_text
         return Content(
             "text",
-            text=self.text + other.text,  # type: ignore[attr-defined, operator]
+            text=combined_text,
             annotations=_combine_annotations(self.annotations, other.annotations),
             additional_properties=_combine_additional_props(self.additional_properties, other.additional_properties),
             raw_representation=_combine_raw_representations(self.raw_representation, other.raw_representation),
@@ -1644,7 +1647,7 @@ def _add_function_call_content(self, other: Content) -> Content:
             arguments = self_arguments
         elif isinstance(self_arguments, str) and isinstance(other_arguments, str):
             arguments = self_arguments + other_arguments
-        elif isinstance(self_arguments, dict) and isinstance(other_arguments, dict):
+        elif isinstance(self_arguments, Mapping) and isinstance(other_arguments, Mapping):
             arguments = {**self_arguments, **other_arguments}
         else:
             raise TypeError("Incompatible argument types")
diff --git a/python/packages/core/tests/core/test_types.py b/python/packages/core/tests/core/test_types.py
index a6797b30449..ff6f9d89b35 100644
--- a/python/packages/core/tests/core/test_types.py
+++ b/python/packages/core/tests/core/test_types.py
@@ -676,6 +676,14 @@ def test_function_call_content_add_merging_and_errors():
     c = a + b
     assert c.arguments == {"x": 1, "y": 2}
 
+    # mapping merge
+    from types import MappingProxyType
+
+    a = Content.from_function_call(call_id="1", name="f", arguments=MappingProxyType({"x": 1}))
+    b = Content.from_function_call(call_id="1", name="f", arguments={"y": 2})
+    c = a + b
+    assert c.arguments == {"x": 1, "y": 2}
+
     # informational_only is preserved across streamed chunks
     a = Content.from_function_call(call_id="1", name="f", arguments='{"x":', informational_only=True)
     b = Content.from_function_call(call_id="1", name="f", arguments="1}")
@@ -2235,6 +2243,22 @@ def test_text_content_iadd_coverage():
     assert t1.additional_properties == {"key1": "val1", "key2": "val2"}
 
 
+def test_text_content_add_handles_none_text():
+    """Test TextContent __add__ when one or both text fields are None."""
+    t_none = Content("text", text=None)
+    t_str = Content.from_text("hello")
+
+    res1 = t_none + t_str
+    assert res1.text == "hello"
+
+    res2 = t_str + t_none
+    assert res2.text == "hello"
+
+    t_none2 = Content("text", text=None)
+    res3 = t_none + t_none2
+    assert res3.text is None
+
+
 def test_text_reasoning_content_add_coverage():
     """Test TextReasoningContent __add__ method for better coverage."""