Check is a variable is not empty : Could someone please let me know how I check is a variable is empty?

I have a variable called `new_date`.  I am reading dates into this variable but sometimes there is no date read in (the date does not exist).  I want to check  if the variable new_date is empty and do something different if there is not date in the variable

e.g.

I have the code below which first checks if variable `picked` is less than variable `prev_final` and `new_date` is a date. 

    if (picked < prev_final) & isinstance(new_date, pd.datetime) 
                # add the value from NEW_DATE
                list_final.append(new_date) 
                # and update the prev_final for the next iteration of the loop
                prev_final = new_date 
            else: # same idea if conditions not met
                list_final.append(picked)
                prev_final = picked 

to this first line I would like to add a condition that `new_date` also must have a date (not empty).  If its empty I'd like the code to use the else i.e. if new_date is empty I would like the code to drop down to where I append `picked` to the `list_final` and `prev_final` and not append `new_date`)

e.g. 

    if (picked < prev_final) & isinstance(new_date, pd.datetime) & (new_date isnot empty)

But I just need to know how to check if new_date is empty.

Any help would be much appreciated.

Thanks