fix: address Copilot review comments

Author: bhumikadangayach

instrumentation/opentelemetry-instrumentation-genai-langchain/src/opentelemetry/instrumentation/genai/langchain/callback_handler.py

@@ -233,10 +233,10 @@ def on_chat_model_start(
             top_p = params.get("top_p")
             frequency_penalty = params.get("frequency_penalty")
             presence_penalty = params.get("presence_penalty")
-            stop_sequences = params.get("stop") or params.get("stop_sequences")
+            stop_sequences = params.get("stop") if params.get("stop") is not None else params.get("stop_sequences")
             seed = params.get("seed")
             temperature = params.get("temperature")
-            max_tokens = params.get("max_completion_tokens") or params.get("max_tokens")
+            max_tokens = params.get("max_completion_tokens") if params.get("max_completion_tokens") is not None else params.get("max_tokens")
 
         provider = "unknown"
         if metadata is not None:

instrumentation/opentelemetry-instrumentation-genai-langchain/tests/test_llm_call.py

@@ -198,7 +198,7 @@ def test_chat_anthropic_claude_sonnet_llm_call(
     spans = span_exporter.get_finished_spans()
     assert len(spans) == 1
     span = spans[0]
-    assert span.attributes.get("gen_ai.request.model") == "claude-sonnet-4-5"
+    assert span.attributes.get(gen_ai_attributes.GEN_AI_REQUEST_MODEL) == "claude-sonnet-4-5"
 
 
 # span_exporter, start_instrumentation, gemini are coming from fixtures defined in conftest.py