/PATTERN/,/^$/{/^$/d; p}
/PATTERN/,/^$/ match lines from PATTERN to empty line.
{/^$/d; p} remove (d) the lines being on ^$ format, print (p) the rest.
WHERE some_col > ''
Since null > '' produces unknown, this has the effect of filtering out both null and empty strings.
@JoshPinter: coalesce(some_col, '') = ''