union_source() doesn't return anything

Would you please help me with that?

```
06:56:41 Database Error in model stg_tpch_orders (models/staging/tpch/stg_tpch_orders.sql)
06:56:41 syntax error at or near ")"
06:56:41 LINE 16: ),
06:56:41 ^
06:56:41 compiled Code at target/run/IO/models/staging/tpch/stg_tpch_orders.sql
```

when I look at the compiled stg_tpch_orders.sql I see that source was not defined at all for some reason and I can't understand why
```
with source as (

),

cleanup as (

select

*,
REGEXP_SUBSTR(_customer_schema, '[0-9]+')::integer as comp_id

from source

)

select * from cleanup
```