Re: v13 planner ERROR: could not determine which collation to use for string comparison

Reproducer:

postgres=# CREATE TABLE t AS SELECT ''a FROM generate_series(1,99); CREATE TABLE u AS SELECT ''a FROM
generate_series(1,99); VACUUM ANALYZE t,u;
 
postgres=# explain SELECT * FROM t JOIN u ON t.a!=u.a;
ERROR:  could not determine which collation to use for string comparison
HINT:  Use the COLLATE clause to set the collation explicitly.