Postgres - Return default value if regex match fails

I'd like to attempt a regex match, and return null if it fails. The following query attempts to find the first number in a string. The result ignores the entry with text 'blah'. I'd prefer it to return a null value instead. This question is probably less about regex and more about set algebra. My hunch is that there is an elegant way to do it, without needing to left join anything, though googling is proving futile. with test_data as ( select 'abc 123' as txt union select 'abc 456' as txt union select 'blah' as txt ) select txt, (regexp_matches(txt, '\d+')) as first_num from test_data