When choose the "--" item for enum array, the parameter is sent with empty value.

[tedyu002]

#5095 # Q&A (please complete the following information)

• OS: Windows 10
• Browser: chrome
• Version: 80.0.3987.163
• Method of installation: dist assets
• Swagger-UI version: 3.25.0
• Swagger/OpenAPI version: OpenAPI 3.0.2

Content & configuration

Example Swagger/OpenAPI definition:

openapi: 3.0.2
info:
  title: API
  description: API
  version: '0.1'
paths:
  /function:
    get:
      parameters:
        - description: items
          required: false
          schema:
            title: item
            type: array
            items:
              enum:
                - first_item
                - second_item
              type: string
            description: item
          name: item
          in: query
      responses:
        '200':
          description: Successful Response
          content:
            application/json:
              schema:
                type: string

Swagger-UI configuration options:

    const ui = SwaggerUIBundle({
        url: '/openapi.json',
    oauth2RedirectUrl: window.location.origin + '/docs/oauth2-redirect',
        dom_id: '#swagger-ui',
        presets: [
        SwaggerUIBundle.presets.apis,
        SwaggerUIBundle.SwaggerUIStandalonePreset
        ],
        layout: "BaseLayout",
        deepLinking: true
    })

?yourQueryStringConfig

Describe the bug you're encountering

When choose "--" of the multiple-select box (produced by enum Array).
The parameter should not be in the query string, but "item=" is in the query string.

To reproduce...

Steps to reproduce the behavior:

1. Go to /function
2. Click on "--" in the item parameter
3. Execute
4. See error

Expected behavior

no item in the query string.

Screenshots

Additional context or thoughts

[hkosova]

Duplicate of #5176.