attempt to set an attribute on NULL in R :     Error in data.table::rbindlist(.data, ...) : 
      attempt to set an attribute on NULL

I am getting this error at:

    FBInsightsExpanded <<- list.stack(list.select(FBInsightsExpanded, website_purchase_roas = website_purchase_roas$action_link_click_destination));
      print(FBInsightsExpanded)
This is what the DF looks like. I am guessing I need to replace NULLs with NA's. But not able to get a fix for it so far

     website_purchase_roas  date_stop
    1    0.673001 offsite_conversion.fb_pixel_purchase, 6.506892 2018-10-11
    2    1.369035 offsite_conversion.fb_pixel_purchase, 0.594109 2018-10-11
    3    2.084238                                           NULL 2018-10-11
    4     1.31209                                           NULL 2018-10-11
    5    2.337662                                           NULL 2018-10-11
    6    0.996678                                           NULL 2018-10-11
    7    1.936385 offsite_conversion.fb_pixel_purchase, 1.482508 2018-10-11
    8    2.777778                                           NULL 2018-10-11
    9           0                                           NULL 2018-10-11
    10   1.994885                                           NULL 2018-10-11
    11   2.402023                                           NULL 2018-10-11
    12   4.635056 offsite_conversion.fb_pixel_purchase, 5.222421 2018-10-11
    13          0                                           NULL 2018-10-11
    14   1.990291                                           NULL 2018-10-11
    15   6.557377                                           NULL 2018-10-11
    16   3.703704                                           NULL 2018-10-11
    17   3.038936                                           NULL 2018-10-11

