Define a #play2 #form #constraint for #required #optional mapping

Constraints.scala

import play.api.data.validation._

trait Constraints {
  /**
   * Defines a ‘required’ constraint for `Optional` values, i.e. one in which None are invalid.
   *
   * '''name'''[constraint.required]
   * '''error'''[error.required]
   */
  def nonNone[A]: Constraint[Option[A]] = Constraint[Option[A]]("constraint.required") { o =>
    if (o.isEmpty) Invalid(ValidationError("error.required")) else Valid
  }
}

Why use Option if you don’t want an optional value?