PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/nestjs/nest/blob/master/CONTRIBUTING.md
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Other... Please describe:

What is the current behavior?

When using enum: undefined on an array property:

@ApiProperty({
  type: 'string',
  isArray: true,
  enum: undefined
})
testStringArray: string[];

the resulting schema incorrectly becomes:

{
  "testStringArray": {
    "type": "array",
    "items": {
      "type": "number",
      "enum": []
    }
  }
}

This is similar to the bug fixed in #3232, but was not fixed for the case where the property is an array.

Issue Number: N/A

What is the new behavior?

After this fix the resulting schema correctly becomes:

{
  "testStringArray": {
    "type": "array",
    "items": {
      "type": "string"
    }
  }
}

Does this PR introduce a breaking change?

• Yes
• No

Other information