// check for omitted fields
	zb0001Len := uint32(18)
	var zb0001Mask uint32 /* 18 bits */
	_ = zb0001Mask
	if z.PartIndices == nil {
		zb0001Len--
		zb0001Mask |= 0x2000
	}
	// variable map header, size zb0001Len
	err = en.WriteMapHeader(zb0001Len)
	if err != nil {
		return
	}
	if zb0001Len == 0 {
		return
	}
	// write "ID"