fix(tracing): Respect explicit empty top-level ignore_spans

An explicit top-level ignore_spans=[] was treated as unset, letting
_experiments rules leak through. Use an is-not-None check so top-level
config wins whenever provided, including an empty list meant to disable
ignoring.

Author: ericapisani

sentry_sdk/tracing_utils.py

@@ -1659,7 +1659,11 @@ def is_ignored_span(name: str, attributes: "Optional[Attributes]") -> bool:
         "ignore_spans"
     )
 
-    ignore_spans = is_ignored_at_top_level or is_ignored_in_experiment_config
+    ignore_spans = (
+        is_ignored_at_top_level
+        if is_ignored_at_top_level is not None
+        else is_ignored_in_experiment_config
+    )
 
     if not ignore_spans:
         return False

tests/tracing/test_span_streaming.py

@@ -1828,6 +1828,30 @@ def test_ignore_spans_top_level_with_trace_lifecycle_in_experiments(
     assert span["name"] == "not ignored"
 
 
+def test_ignore_spans_empty_top_level_overrides_experiments(sentry_init, capture_items):
+    # An explicit empty top-level ignore_spans should disable ignoring,
+    # taking precedence over any rules set in _experiments.
+    sentry_init(
+        traces_sample_rate=1.0,
+        trace_lifecycle="stream",
+        ignore_spans=[],
+        _experiments={"ignore_spans": ["ignored"]},
+    )
+
+    items = capture_items("span")
+
+    with sentry_sdk.traces.start_span(name="ignored") as span:
+        assert span.sampled is True
+        assert isinstance(span, StreamedSpan)
+
+    sentry_sdk.get_client().flush()
+    spans = [item.payload for item in items]
+
+    assert len(spans) == 1
+    (span,) = spans
+    assert span["name"] == "ignored"
+
+
 @pytest.mark.parametrize(
     ("options", "streaming_enabled"),
     [