openapi - regex for not allowing whitespace or hyphen

Question

Am using openapi 3.0.3 to autogenerate my Spring Boot based REST API...

Inside src/main/resources/openapi/schema/PurchaseOrder.yaml:

openapi: '3.0.3'
info:
  title: 'Purchase Order'  
  version: '1.0'
paths: {}

components:
  schemas:
    PurchaseOrder:
      title: 'Purchase Order'
      type: 'object'
      properties:
        account:
          type: 'string'
          description: Identifier for account making the purchase
          example: 1
          minLength: 1
          pattern: '^\s-$'

---

So, I need it to include alphanumeric values but no whitespaces (tried using this pattern: '^\s-$') - can't have whitespaces at all...

When trying:

{
    account: 'a b'
}

This is what I received as a JSON Response:

"validationErrors": [
  {
    "field": "account",
    "message": "must match \"^\\s-$\""
  }
]

---

This same validation error also happens when I try a valid JSON (containing more than one char and no whitespaces and no hyphens):

{
   'account': 'ab'
}

This should have been valid and not thrown any validation errors...

---

How can I enforce no whitespaces and/or no hyphens at all using regex inside this yaml file?