fix(usage): Handle None values in token details when adding usage

The Usage.add() method was failing when token detail fields
(cached_tokens, reasoning_tokens) were None. This occurs when using
providers like Ollama that don't provide these optional fields.

Added defensive handling to treat None as 0, matching the pattern
used elsewhere in the codebase (openai_chatcompletions.py,
litellm_model.py, chatcmpl_stream_handler.py).

Signed-off-by: Adrian Cole <[email protected]>

Author: codefromthecrypt

examples/financial_research_agent/agents/model.py

@@ -73,13 +73,13 @@ def add(self, other: "Usage") -> None:
         self.output_tokens += other.output_tokens if other.output_tokens else 0
         self.total_tokens += other.total_tokens if other.total_tokens else 0
         self.input_tokens_details = InputTokensDetails(
-            cached_tokens=self.input_tokens_details.cached_tokens
-            + other.input_tokens_details.cached_tokens
+            cached_tokens=(self.input_tokens_details.cached_tokens or 0)
+            + (other.input_tokens_details.cached_tokens or 0)
         )
 
         self.output_tokens_details = OutputTokensDetails(
-            reasoning_tokens=self.output_tokens_details.reasoning_tokens
-            + other.output_tokens_details.reasoning_tokens
+            reasoning_tokens=(self.output_tokens_details.reasoning_tokens or 0)
+            + (other.output_tokens_details.reasoning_tokens or 0)
         )
 
         # Automatically preserve request_usage_entries.

src/agents/usage.py

@@ -267,3 +267,31 @@ def test_anthropic_cost_calculation_scenario():
     for req in usage.request_usage_entries:
         assert req.input_tokens < 200_000
         assert req.output_tokens < 200_000
+
+
+def test_usage_add_handles_none_token_details():
+    u1 = Usage(
+        requests=1,
+        input_tokens=10,
+        input_tokens_details=InputTokensDetails(cached_tokens=3),
+        output_tokens=20,
+        output_tokens_details=OutputTokensDetails(reasoning_tokens=5),
+        total_tokens=30,
+    )
+    u2 = Usage(
+        requests=2,
+        input_tokens=15,
+        output_tokens=25,
+        total_tokens=40,
+    )
+    u2.input_tokens_details.cached_tokens = None
+    u2.output_tokens_details.reasoning_tokens = None
+
+    u1.add(u2)
+
+    assert u1.requests == 3
+    assert u1.input_tokens == 25
+    assert u1.output_tokens == 45
+    assert u1.total_tokens == 70
+    assert u1.input_tokens_details.cached_tokens == 3
+    assert u1.output_tokens_details.reasoning_tokens == 5