JSON of mac_payload misses f_cnt in case of 0

[pbttn2019]

after changing the battery of an ABP device I found that the initial framecounter 0 is missing in the JSON structure:

frame 0:

data": {
    "@type": "type.googleapis.com/ttn.lorawan.v3.GatewayUplinkMessage",
    "message": {
       ...
        "mac_payload": {
          "f_hdr": {
            "dev_addr": "***",
            "f_ctrl": {}
          },
          "f_port": 1,
          "frm_payload": "***"
        }
      },

frame 1 and sucessors have the f_cnt entry:

  "data": {
    "@type": "type.googleapis.com/ttn.lorawan.v3.GatewayUplinkMessage",
    "message": {
      ...
         "mac_payload": {
          "f_hdr": {
            "dev_addr": "26011480",
            "f_ctrl": {},
            "f_cnt": 1
          },
          "f_port": 1,
          "frm_payload": "***"
        }
      },

Is this a bug or an (un)documented feature?

[kersing (Jac Kersing)]

Have you tried forum search? This has been called out a couple of years ago already: First f_cnt is empty/null - world wide technical debt in progress

[pbttn2019]

Did a search, but potentially used wrong keywords. Thank you for the hint!