postgres array question

I am parsing log files and storing them in postgres. I find that I cannot
append an element into a null array with array_append. The only way that
appeared to me is to first query the array to find if it is null and use a
different syntax if it is null and use array_append otherwise. This was
initially OK, but I guess this would decrease the performance by a factor of
2 (because of the initial query). I am trying to load in several thousands
of log files and the process has been running overnight and did not
complete. Any suggestions on optimizing this process would be greatly
appreciated.

Thanks,
George