`na_matches = "na"` doesn't work for DuckDB

[mgirlich]

library(dbplyr)
library(dplyr, warn.conflicts = FALSE)

con <- DBI::dbConnect(duckdb::duckdb())
x <- copy_to(
  src_dbi(con),
  tibble(x = 1),
  name = "dummy"
)
left_join(x, x, by = "x", na_matches = "na") %>% 
  show_query()
#> <SQL>
#> SELECT "LHS"."x" AS "x"
#> FROM "dummy" AS "LHS"
#> LEFT JOIN "dummy" AS "RHS"
#> ON (CASE WHEN ("LHS"."x" = "RHS"."x") OR ("LHS"."x" IS NULL AND "RHS"."x" IS NULL) THEN 0 ELSE 1 = 0)
left_join(x, x, by = "x", na_matches = "na")
#> Error in .local(conn, statement, ...): duckdb_prepare_R: Failed to prepare query SELECT *
#> FROM (SELECT "LHS"."x" AS "x"
#> FROM "dummy" AS "LHS"
#> LEFT JOIN "dummy" AS "RHS"
#> ON (CASE WHEN ("LHS"."x" = "RHS"."x") OR ("LHS"."x" IS NULL AND "RHS"."x" IS NULL) THEN 0 ELSE 1 = 0)
#> ) "q01"
#> LIMIT 11
#> Error: Parser Error: syntax error at or near ")"
#> LINE 5: ...LEFT JOIN "dummy" AS "RHS"
#> ON (CASE WHEN ("LHS"."x" = "RHS"."x") OR ("LHS"."x" IS NULL AND "RHS"."x" IS NULL) THEN 0 ELSE 1 = 0)
#>                                                   ^

^{Created on 2021-09-17 by the reprex package (v2.0.1)}