Workflow is not able start, rule is failing validation

Hi Team,
Please find the Workflow details
Meta data:

[07:23:05] root@ded-95.opsteam1:/opt/stackstorm/packs/default/actions/workflows# cat ../event_demo.meta.yaml
pack: default
enabled: true
runner_type: orquesta
parameters:
  alerts_hostname:
    type: object
    required: true
  alerts_id:
    type: object
    required: true
  alerts_command:
    type: string
    required: true
  resolver:
    type: string
    required: true
name: event_demo
entry_point: workflows/event_demo.yaml
[07:23:16] root@ded-95.opsteam1:/opt/stackstorm/packs/default/actions/workflows#

WF:

    version: 1.0
input:
  - alerts_hostname
  - alerts_id
  - alerts_command
  - resolver

tasks:
  output_alert:
    action: core.echo
    with:
      concurrency: 1
    input:
      message: "Alert hostname <% ctx().alerts_hostname %>, alert id <% ctx().alerts_id, command exec <% ctx('alerts_command') %>, resolver <% ctx('resolver') %>"

can someone guide me i want to print the values which i am getting in input to the WF.

Initially its giving an error like

    {
  "output": null,
  "errors": [
    {
      "type": "error",
      "message": "TypeError: argument of type 'NoneType' is not iterable",
      "task_id": "output_alert",
      "route": 0
    }
  ]
}

Your tasks has with syntax which If I remember correctly must have items which are array or list like iterables. if that is not the input, please remove them. with and concurrency are not valid in the current structure.