Dynamic block with nested map

Hello, hope someone can help me to develop condition for dynamic block. I’m trying to create a code for generating optional warning threshold in newrelic_nrql_alert_condition (newrelic provider). I’m using nested map for supplying argument values:

nr_nrql_condition = {
  "nrql1" = {
    policy = "policy1"
    query  = "SELECT average(duration) FROM Transaction where appName = 'App1'"
    critical_threshold = {
      operator              = "above"
      threshold             = 3
      threshold_duration    = 300
      threshold_occurrences = "all"
    }
    warning_threshold = {
      operator              = "above"
      threshold             = 1
      threshold_duration    = 300
      threshold_occurrences = "all"
    }
  },
  "nrql2" = {
    policy = "policy1"
    query  = "SELECT average(duration) FROM Transaction where appName = 'App2'"
    critical_threshold = {
      operator              = "above"
      threshold             = 7
      threshold_duration    = 300
      threshold_occurrences = "all"
    }
    warning_threshold = {}
  },
}

and the below is the extract of the code for creating the resource

resource "newrelic_nrql_alert_condition" "foo" {
  for_each    = var.nr_nrql_condition

  ...

  critical {
    operator              = lookup(each.value["critical_threshold"], "operator")
    threshold             = lookup(each.value["critical_threshold"], "threshold")
    threshold_duration    = lookup(each.value["critical_threshold"], "threshold_duration")
    threshold_occurrences = lookup(each.value["critical_threshold"], "threshold_occurrences")
  }

  dynamic "warning" {
    for_each = each.value["warning_threshold"] != {} ? [1] : []
    content {
      operator              = lookup(each.value["warning_threshold"], "operator")
      threshold             = lookup(each.value["warning_threshold"], "threshold")
      threshold_duration    = lookup(each.value["warning_threshold"], "threshold_duration")
      threshold_occurrences = lookup(each.value["warning_threshold"], "threshold_occurrences")
    }
  }
}

dynamic "warning" block only works if warning_threshold map is defined with valid key/values parameters. I’m struggling to find a way to create condition to skip "warning" block if warning_threshold = {}