Postgres to R date conversion and Writing NULL to postgres database using RpgSQL issue

Please comment on thses two queries.

1) While converting field of data type "date" selected form postgres,
RpgSQL gives error on windows  when field value is null.
2) How a field can be assigned NULL value in R . I couldn't found a way to
write NULL value in database table row using RpgSQL. I used dbWriteTable
function to write data to database. One workaround temporarily i did is to
write "NULL" string in database and then update "NULL" to NULL using update
SQL script.

Thanks & Regards,
Subodh Agrawal