fix setting trace_id

Author: sentrivana

sentry_sdk/client.py

@@ -977,15 +977,15 @@ def _capture_metric(self, metric):
             metric["attributes"]["sentry.release"] = release
 
         span = sentry_sdk.get_current_span()
-        trace_id = "00000000-0000-0000-0000-000000000000"
+        metric["trace_id"] = "00000000-0000-0000-0000-000000000000"
 
         if span:
-            metric["trace_id"] = span.trace_id or trace_id
-            metric["span_id"] = span.span_id or None
+            metric["trace_id"] = span.trace_id
+            metric["span_id"] = span.span_id
         else:
             propagation_context = isolation_scope.get_active_propagation_context()
             if propagation_context:
-                metric["trace_id"] = propagation_context.trace_id or trace_id
+                metric["trace_id"] = propagation_context.trace_id
 
         if isolation_scope._user is not None:
             for metric_attribute, user_attribute in (