Array of hashes not failing correctly when array is empty

grape: 1.0.1
ruby: 2.4.2

When you have:

params do
          requires :paired_values, type: Array do
            requires :name, allow_blank: false, type: String
            requires :semver, allow_blank: false, type: String, semver_constraint: true
          end
        end

And semver_constraint custom validator looks like

class SemverConstraint < Grape::Validations::Base
  def validate_param!(attr_name, params)
    Semverse::Constraint.new(params[attr_name])
  rescue Semverse::InvalidConstraintFormat => e
    raise Grape::Exceptions::Validation, params: [@scope.full_name(attr_name)], message: e.message
  end
end

When you call into the api_endpoint with params: { paired_values: [] } grape ends up calling validate_param! with attr_name being :semver and params being "", so this throws the exception TypeError: no implicit conversion of Symbol into Integer. Because these values are required shouldn't the grape validation for required fail out before this is even called?

I can easily work around this but before i upgraded to 1.0.0/1.0.1 this was not throwing this exception.

Start by reproducing the issue from the parameter declaration and custom SemverConstraint validator shown in the report with paired_values set to an empty array. Trace the validation order for the required fields and confirm that the required validation fails before the custom validator runs; done means the expected validation error is raised instead of the TypeError.