title: NestJs Swagger mixed types
body: <p>I have a class that one of the properties can be string or array of strings, not sure how should I define it in swagger</p>
  <pre><code>    @ApiProperty({
          description: `to email address`,
          type: ???, &lt;- what should be here?
          required: true,
      })
      to: string | Array&lt;string&gt;;
  </code></pre>
  <p>I tried</p>
  <pre><code>    @ApiProperty({
          description: `to email address(es)`,
          additionalProperties: {
              oneOf: [
                  { type: 'string' },
                  { type: 'Array&lt;string&gt;' },
              ],
          },
          required: true,
      })
  </code></pre>
  <p>and</p>
  <pre><code>    @ApiProperty({
          description: `to email address(es)`,
          additionalProperties: {
              oneOf: [
                  { type: 'string' },
                  { type: 'string[]' },
              ],
          },
          required: true,
      })
  </code></pre>
  <p>and</p>
  <pre><code>    @ApiProperty({
          description: `to email address(es)`,
          additionalProperties: {
              oneOf: [
                  { type: 'string' },
                  { type: '[string]' },
              ],
          },
          required: true,
      })
  </code></pre>
  <p>but the result is like below image, which is not correct</p>
  <p><a href="https://i.stack.imgur.com/NWyig.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/NWyig.png" alt="enter image description here" /></a></p>