var value =
    {
      parts: {
        field: {
          headers: {
            "Content-Disposition": {
              name: "field"
            }
          },
          content: "value"
        }
      }
    }

type Multipart = {
  parts: {
    field: {
        content: Any
    }
  }
}
---
{
  a: value match {
    case is Multipart -> "OK"
    else -> "BAD"
  }
}