metrics: make null values passed to repeated fields more obvious am: 0b1579a826 am: 3f4225949a am: 33ef221104 am: 67e2030273
metrics: make null values passed to repeated fields more obvious am: 0b1579a826 am: 3f4225949a am: 33ef221104 am: 67e2030273

Change-Id: Iea884ba2932195da33145b539cd3e36f72f00cf8

google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto