[NTG-context] metapost boxes error

Is there a different approach to use boxes.mp? MNWE: \startMPpage input boxes.mp; boxit.bl("left"); boxit.br("right"); br.sw - bl.ne = (20,0); drawboxed(bl,br); \stopMPpage LOG snippets: system > ConTeXt ver: 2020.04.10 19:11 MKIV beta fmt: 2020.4.19 int: english/english metapost log > loading metafun, including plain.mp version 1.004 for metafun iv and xl metapost log > metapost log > >> _dojoin metapost log > ! Isolated expression.