custom read_array_of_string method dies

proto.rb

class FFI::Pointer
  # This works fine on MRI, but dies on JRuby
  def read_array_of_string
    elements = []

    psz = RUBY_PLATFORM == 'java' ? 4 : self.class.size
    loc = self

    until ((element = loc.read_pointer).null?)
      elements << element.read_string
      loc += psz
    end

    elements
  end
end