The context of the problem is the validation of queries with a LIMIT clause but no ORDER BY, e.g. "SELECT c FROM t LIMIT 2".
The problem does not show up at parsing time but when running a validator. The generated AST includes an ORDER BY operand with an empty column list.
When building a SQL query out of the validated AST, an ORDER BY clause is inserted before the LIMIT/FETCH clause, e.g "SELECT c FROM t ORDER BY LIMIT 2". This SQL query is not valid.