Checking empty array

Dear all,

What is the correct way to check whether an array is empty?
I have an array which I initialize with '{}' and then do som array_append
under some circonstances. I would like to know whether the array is empty at
the end of the function. I have not found the answer in the help page nor on
the web. I use the keyword isnull but that does not seem to work in all the
cases.
I would appreciate if someone could put this piece of information into the
Postgres documentation.

Here is what I do, in pseudo-code:

myarray varchar[];
myarray := '{}';

FOR ___ LOOP
IF (___) THEN
myarray := array_append(myarray, somestuff);
END IF;
END LOOP;

-- Is my array empty now?
IF (myarray isnull) THEN
__
END IF;

Regards,
Alexis Beuraud