Target attribute on menus breaks HTML validation

[sarahelsaig]

Describe the bug

Since target attribute has been added to menu links (#15541) validation via html-validate fails. This is because if there is no target specified, it creates an empty attribute, like <a class="nav-link px-lg-3 py-3 py-lg-4" href="/" target="">Home</a>. This is not valid. If there is no target specified, the attribute should be omitted.

Note: according to MDN the default is target="_self" so falling back to that value is also acceptable when omitting the target attribute would be complicated.

Orchard Core version

Latest preview, at least TheBlogTheme package is affected.

Expected behavior

Menu should produce valid HTML.

Logs and screenshots

An example entry of the validation report:

{
  "ruleId": "attribute-allowed-values",
  "severity": 2,
  "message": "Attribute \"target\" has invalid value \"\"",
  "offset": 2331,
  "line": 55,
  "column": 6,
  "size": 1,
  "selector": "#navbarResponsive > ul > li:nth-child(2) > a",
  "ruleUrl": "https://html-validate.org/rules/attribute-allowed-values.html",
  "context": {
    "element": "a",
    "attribute": "target",
    "value": "",
    "allowed": {
      "enum": [
        {},
        "_blank",
        "_self",
        "_parent",
        "_top"
      ]
    }
  }
}

[hishamco]

/cc @hyzx86

[hyzx86]

@sarahelsaig Looks like we're duplicating our work~

[github-actions]

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