chore(tracer): handle None in activate_distributed_headers (#13329)

The function `activate_distributed_headers` unconditionally calls

`context = HTTPPropagator.extract(request_headers)`

and then immediately does` context.trace_id`, but under some
circumstances (e.g. no distributed-trace headers present) `extract()`
can return `None`. This leads to an uncaught

`AttributeError: 'NoneType' object has no attribute 'trace_id'`. 


Fixes issue: #13277

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Author: rachelyangdog

ddtrace/contrib/internal/trace_utils.py

@@ -510,7 +510,9 @@ def activate_distributed_headers(tracer, int_config=None, request_headers=None,
 
     if override or (int_config and distributed_tracing_enabled(int_config)):
         context = HTTPPropagator.extract(request_headers)
-
+        # bail out if no context was extracted
+        if context is None:
+            return None
         # Only need to activate the new context if something was propagated
         # The new context must have one of these values in order for it to be activated
         if not context.trace_id and not context._baggage and not context._span_links:

tests/tracer/test_trace_utils.py

@@ -22,6 +22,7 @@
 from ddtrace.internal.compat import ensure_text
 from ddtrace.propagation.http import HTTP_HEADER_PARENT_ID
 from ddtrace.propagation.http import HTTP_HEADER_TRACE_ID
+from ddtrace.propagation.http import HTTPPropagator
 from ddtrace.settings import IntegrationConfig
 from ddtrace.settings._config import Config
 from ddtrace.trace import Context
@@ -974,6 +975,15 @@ def test_activate_distributed_headers_no_headers(int_config, tracer):
     assert tracer.context_provider.active() is None
 
 
+@mock.patch.object(HTTPPropagator, "extract", return_value=None)
+def test_activate_distributed_headers_missing_headers(int_config, tracer):
+    # Verify that when HTTPPropagator.extract returns None (no incoming headers),
+    # activate_distributed_headers returns early without error and leaves the tracer’s context empty.
+    int_config.myint["distributed_tracing_enabled"] = True
+    trace_utils.activate_distributed_headers(tracer, int_config=int_config.myint, request_headers=None, override=True)
+    assert tracer.context_provider.active() is None
+
+
 def test_activate_distributed_headers_override_true(int_config, tracer):
     int_config.myint["distributed_tracing_enabled"] = False
     headers = {