Make sure future::cancel() is imported conditionally

Author: HenrikBengtsson

DESCRIPTION

@@ -1,5 +1,5 @@
 Package: future.mirai
-Version: 0.2.2-9215
+Version: 0.2.2-9216
 Depends:
     future (>= 1.40.0)
 Imports:

R/001.import_future_functions.R

@@ -26,8 +26,8 @@ import_future_functions <- function() {
   getFutureBackendConfigs <<- import_future("getFutureBackendConfigs")
 
   ## Until future (>= 1.49.0) is on CRAN
-  cancel <<- import_future("cancel", default = NULL)
-  if (is.null(cancel)) {
+  cancel <<- import_future("cancel", default = NA)
+  if (is.na(cancel)) {
     interrupt <- import_future("interrupt")
     cancel <<- function(x, interrupt = TRUE, ...) {
       if (!interrupt) return(x)