concatenation operator || with "null" array

Hello!

When I try to fill an array with the concatenation operator, like
UPDATE test SET myint = myint || ARRAY[123] WHERE id = 1
that before that statement was null, then it is also null after that
statement.
But if there is already something in that array and I execute that
statement, then everything works fine and one can find the 123 there,
too.
Is this the normal behavior? Is there a way to "concatenate" to null
arrays as well, or do I have to test this inside my script, and if it
is null fill it normal for the first time?

Best regards,
Kai