Date Difference with blank values

Hello,

I have an issure with this code, that calculates the transit time between two dates, when the last date is blank. Is there a way to add a function to that code, so it gives a blank value when one of the two dates are blank?

count = var calendarTable= CALENDAR([Start Date],[End Date])
var exceptDate=CALCULATETABLE(VALUES('Situational Holidays'[situationDate]),FILTER(ALL('Situational Holidays'),[Entity]=EARLIER(Dates[Origin Entity])))
var filtered=ADDCOLUMNS(EXCEPT(calendarTable,exceptDate),"Day Of Week",WEEKDAY([Date],1))
return
COUNTROWS(FILTER(filtered,[Day Of Week]<>6&&[Day Of Week]<>7))