Workflow Template UI - "Empty" workflow template causes error when rendering

[logicfox]

Checklist:

• I've included the version.
• I've included reproduction steps.
• I've included the workflow YAML.
• I've included the logs.

What happened:
When an "empty" WorkflowTemplate is selected from the Workflow Templates summary page, a rendering error occurs.

What you expected to happen:
Page is rendered correctly

How to reproduce it (as minimally and precisely as possible):
Submit this template

apiVersion: argoproj.io/v1alpha1
kind: WorkflowTemplate
metadata:
    name: silly-template
spec:
    templates: []

Navigate to Workflow Templates in the UI

Click on the template

Anything else we need to know?:

Environment:
Kind, AKS, EKS (v1.14 through v.1.17)

• Argo version: 2.7.6
• Kubernetes version : 1.14 - 1.17

Other debugging information (if applicable):
Fetch from browser

fetch("http://localhost:2746/api/v1/workflow-templates/default/silly-template", {
  "headers": {
    "accept": "*/*",
    "accept-language": "en-US,en;q=0.9",
    "cache-control": "no-cache",
    "pragma": "no-cache",
    "sec-fetch-dest": "empty",
    "sec-fetch-mode": "cors",
    "sec-fetch-site": "same-origin"
  },
  "referrer": "http://localhost:2746/workflow-templates/default/silly-template",
  "referrerPolicy": "no-referrer-when-downgrade",
  "body": null,
  "method": "GET",
  "mode": "cors",
  "credentials": "include"
});

Response

{"metadata":{"name":"silly-template","namespace":"default","selfLink":"/apis/argoproj.io/v1alpha1/namespaces/default/workflowtemplates/silly-template","uid":"98316859-9b65-483a-bead-566dba1d3f20","resourceVersion":"3106","generation":1,"creationTimestamp":"2020-04-29T17:08:11Z","annotations":{"kubectl.kubernetes.io/last-applied-configuration":"{\"apiVersion\":\"argoproj.io/v1alpha1\",\"kind\":\"WorkflowTemplate\",\"metadata\":{\"annotations\":{},\"name\":\"silly-template\",\"namespace\":\"default\"},\"spec\":{\"templates\":[]}}\n"}},"spec":{"templates":null,"arguments":{}}}

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