Not enough byte to read from buffer about gosmpp HOT 5 CLOSED

type SubmitSMResp struct {
	base
	MessageID string
}

// Marshal implements PDU interface.
func (c *SubmitSMResp) Marshal(b *ByteBuffer) {
	c.base.marshal(b, func(b *ByteBuffer) {
		b.Grow(len(c.MessageID) + 1)

		_ = b.WriteCString(c.MessageID)
	})
}

// Unmarshal implements PDU interface.
func (c *SubmitSMResp) Unmarshal(b *ByteBuffer) error {
	return c.base.unmarshal(b, func(b *ByteBuffer) (err error) {
		if c.CommandStatus == data.ESME_ROK {
			c.MessageID, err = b.ReadCString()
		}
		return
	})
}

b.Grow(len(c.MessageID) + 1)

_ = b.WriteCString(c.MessageID)

if len(c.MessageID) > 0 {
      b.Grow(len(c.MessageID) + 1)

      _ = b.WriteCString(c.MessageID)
}