For metric groups, skip metrics in the list that are None. This allows
functions to better optionally return metrics.

Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/perf/pmu-events/metric.py | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/tools/perf/pmu-events/metric.py b/tools/perf/pmu-events/metric.py
index b39189182608..dd8fd06940e6 100644
--- a/tools/perf/pmu-events/metric.py
+++ b/tools/perf/pmu-events/metric.py
@@ -493,13 +493,15 @@ class MetricGroup:
   """
 
   def __init__(self, name: str,
-               metric_list: List[Union[Metric, 'MetricGroup']],
+               metric_list: List[Union[Optional[Metric], Optional['MetricGroup']]],
                description: Optional[str] = None):
     self.name = name
-    self.metric_list = metric_list
+    self.metric_list = []
     self.description = description
     for metric in metric_list:
-      metric.AddToMetricGroup(self)
+      if metric:
+        self.metric_list.append(metric)
+        metric.AddToMetricGroup(self)
 
   def AddToMetricGroup(self, group):
     """Callback used when a MetricGroup is added into another."""
-- 
2.46.1.824.gd892dcdcdd-goog