Here is the KNIME 5.6 version, which adds the much-needed today() and now() function to the Expression node… 
… allowing it to be written similar to @arun_knimer 's Column Expressions example :
if($["MyDate"]== MISSING, "Check"
,if(days_between($["MyDate"],today()) >180, "Del"
,"Keep")
)
Date column condition KNIME 5.6.knwf (50.6 KB)
From the 5.6 changelog:
- AP-24036: Add “now” and “today” Expression functions that returns the current zoned date time (kudos to @HansS for reporting 1)
Thanks @HansS !! 