JRuby Internal Java NegativeArraySizeExcetpion when normalising a string

# -*- encoding : utf-8 -*-
require 'active_support/core_ext'
require 'test/unit'

class String
  def strip_noise()
    return if empty?
    self.force_encoding('utf-8').mb_chars.normalize(:kd).gsub(/[^\x00-\x7F]/n,'').to_s().strip()
  end
end

class StringTests < Test::Unit::TestCase
  def test_strip_illegal_chars()
    assert_equal("", "        \xC2\xA0".strip_noise())
  end
end