MySQL error in file: /engine/modules/show.full.php at line 944

Error Number: 1139

The Error returned was:
Got error 'empty (sub)expression' from regexp

SQL query:

SELECT id, date, short_story, xfields, title, category, alt_name FROM dle_post WHERE category regexp '[[:<:]](15|)[[:>:]]' AND MATCH (title, short_story, full_story, xfields) AGAINST ('Это все еда / The F Word (US) ') AND id != 29762 AND approve=1 AND date < '2018-05-22 14:51:39' LIMIT 10