presto-hive/src/main/java/io/prestosql/plugin/hive/IonSqlQueryBuilder.java/IonSqlQueryBuilder/formatPredicate
class IonSqlQueryBuilder:    private String formatPredicate(String column, String type)
    {
        return format("case %s when '' then null else CAST(%s AS %s) end", column, column, type);
    }