Reject blank input with graphql-ruby

The graphql-ruby gem has a built-in blank validator:

class Mutations::UserUpdate < Mutations::BaseMutation
  null true

  argument :user_id,
    String,
    "Identifier of user",
    required: true,
    validates: {allow_blank: false}

  field :user_id, String, null: false

  def resolve(user_id:)
    {user_id:}
  end
end

So now a mutation with a user_id of " " will cause the graphql response to have an error:

mutation UserUpdate($userId: String!) {
  userUpdate(userId: $userId) {
    userId
  }
}