Not dropping default argument to lag() on Redshift

[louisahsmith]

I am connecting to a redshift db using DatabaseConnector and writing code in dplyr. The lag() function has an argument default = NULL that is not supported by redshift, so it gets dropped by dbplyr (see tidyverse/dbplyr#549.) This is not getting dropped when connecting via DatabaseConnector, resulting in

java.sql.SQLException: [Amazon](500310) Invalid operation: Default parameter not be supported for window function lag;

That is,

con <- DatabaseConnector::connect(
    dbms = "redshift", 
    ...
)
dbplyr::translate_sql(lag(x), con = con)

returns

<SQL> LAG(x, 1, NULL) OVER ()

but should return

<SQL> LAG(`x`, 1) OVER ()

as with dbplyr::translate_sql(lag(x), con = dbplyr::simulate_redshift())

[schuemie]

Should become moot when we switch to native backends (#257)