div(v-drag) 

as in the code above, if the v-drag instruction does not pass a value, the pug will be parsed as Vmurdrag = "v-drag" ,

will throw an error:
[Vue warn]: Property or method "v" is not defined on the instance but referenced during render

in order not to allow him to report an error, you must give him a vacancy, such as vMuthdragcards",
how to correctly resolve him to v-drag