In 7.14 the var_set function in- Canvas no longer accepts the input context as the value. One needs to explicitly set the value now.
Trying to run this expression:
date | var_set "mydate" | var "mydate" | render as="debug"
gives the error message:
[var_set] > args.value is undefined
To get this to work the value needs to be explicitly set i.e.
date | var_set "mydate" value={context} | var "mydate" | render as="debug"