trace creation date sometimes missing

[alban]

Symptoms:

$ kubectl gadget traceloop list
PODNAME           PODUID      INDEX    TRACEID             CONTAINERID    STATUS
multiplication    41f6677e    0        0000055fa8cf3342    85983624       deleted 9 minutes ago
multiplication    679b1343    0        000005d0d786e53e    ba580597       deleted About a minute ago
nginx             bd7983a4    0        0000052a3d3493ec    27a353fc       created a while ago (parsing time "" as "2006-01-02T15:04:05Z07:00": cannot parse "" as "2006")

The json for this nginx trace without creation date is:

   {
      "capabilities" : 136316359,
      "containerid" : "cri-o://27a353fc1074066ba64c8e7cdbf948b362b3aabfd45625a80158bced241b3087",
      "namespace" : "default",
      "node" : "crc-rk2fc-master-0",
      "podname" : "nginx",
      "status" : "ready",
      "traceid" : "0000052a3d3493ec",
      "uid" : "bd7983a4-95b5-11ea-8585-0242ac11003a"
   },

Some other traces have the timecreation field.