amq-protocol encode_properties should not try to encode nil values

gistfile1.rb

def self.encode_properties(body_size, properties)
  pieces, flags = [], 0

  properties.each do |key, value|
    if value
      i, f, result = self.send(:"encode_#{key}", value)
      flags |= f
      pieces[i] = result
    end
  end

  # result = [60, 0, body_size, flags].pack('n2Qn')
  result = [60, 0].pack(PACK_UINT16_X2)
  result += AMQ::Hacks.pack_64_big_endian(body_size)
  result += [flags].pack(PACK_UINT16)
  result + pieces.join(EMPTY_STRING)
end