Modbus default values do not match example config

[Hipska]

Relevant telegraf.conf

# Retrieve data from MODBUS slave devices
[[inputs.modbus]]
  name = "SDM630"
  slave_id = 1
  timeout = "1s"
  controller = "file:///dev/ttyUSB0"
  baud_rate = 9600
  data_bits = 8
  parity = "N"
  stop_bits = 1
  transmission-mode = "RTU"
  debug_connection = true
  configuration_type = "register"
  discrete_inputs = [
    { name = "start",          address = [0]},
    { name = "stop",           address = [1]},
    { name = "reset",          address = [2]},
    { name = "emergency_stop", address = [3]},
  ]

Logs from Telegraf

root@sentinel:/etc/telegraf# telegraf -test -config /etc/telegraf/telegraf.conf
2022-09-17T17:13:59Z I! Starting Telegraf 1.24.0
2022-09-17T17:13:59Z I! Available plugins: 222 inputs, 9 aggregators, 26 processors, 20 parsers, 57 outputs
2022-09-17T17:13:59Z I! Loaded inputs: cpu disk kernel mem modbus net netstat processes swap system
2022-09-17T17:13:59Z I! Loaded aggregators: 
2022-09-17T17:13:59Z I! Loaded processors: 
2022-09-17T17:13:59Z W! Outputs are not used in testing mode!
2022-09-17T17:13:59Z I! Tags enabled: host=sentinel
2022-09-17T17:13:59Z E! [telegraf] Error running agent: could not initialize input inputs.modbus: initializing client failed: invalid protocol 'file' - '' 
root@sentinel:/etc/telegraf#

System info

1.24.0

Docker

No response

Steps to reproduce

Run telegraf with the given config

Expected behavior

Default value for transmission_mode should be "RTU"

Actual behavior

Default value for transmission_mode appears to be empty.

Additional info

No response

[sspaink]

@srebhan do you know if you the README or the code should be updated in this case? It didn't seem like the code has changed recently.

[Hipska]

Another thing, shouldn't telegraf complain about non existing transmission-mode?

[MyaLongmire]

@Hipska do you think discrete_input, holding_registers, input_registers, etc. need to also default to what is in the readme?

[Hipska]

I don't actually use Modbus, this was found because of interaction in the community Slack. You should ask @srebhan for this.