# File lib/nice-ffi/library.rb, line 178
  def optional( warn_message=nil, &block )
    raise LocalJumpError, "no block given" unless block_given?
    begin
      block.call()
    rescue FFI::NotFoundError => e
      if warn_message
        puts warn_message
      else
        puts "Warning: #{e.message}"
      end
    end
  end