Table: afc_champs_league
Columns: season
team_1
score
team_2
venue

Question: What year did Bangkok University and Chunnam Dragons have a score of 0-0?
SQL: SELECT SUM("season") FROM afc_champs_league WHERE "team_1" = 'bangkok university' AND "score" = '0-0' AND "team_2" = 'chunnam dragons'