There are several ways to check

whether a list is empty, e.g.

eval isnull(varname(somelist)

eval somelist=null

eval nelem(list)

1) Which way is the most efficient/ recommended ?

Also, the behavior of null keyword is different

with lists and strings, for example

somelist = null 

is evaluated but

eval somestring = null

outputs

Data types not conformable for operation

2) Is there a compact text on null keyword?

I can imagine the following way to use isnull():

Suppose, I want to write a function which

creates new variables with automated names.

isnull() could be used for checking duplicated names.

3) What are main uses of isnull()

Oleh