Copy out wording

Our documentation for COPY
(http://www.postgresql.org/docs/8.4/static/sql-copy.html) has the
following to say:
"
The CSV format has no standard way to distinguish a NULL value from
an empty string. PostgreSQL's COPY handles this by quoting. A NULL is
output as the NULL string and is not quoted, while a data value
matching the NULL string is quoted. Therefore, using the default
settings, a NULL is written as an unquoted empty string, while an
empty string is written with double quotes (""). Reading values
follows similar rules. You can use FORCE NOT NULL to prevent NULL
input comparisons for specific columns.
"

Shouldn't that be:
"A NULL is output as the NULL string and is not quoted, while a data
value matching the empty string is quoted"?

If not, then what really is the difference between a NULL and a NULL string?

--
Magnus Hagander
Me: http://www.hagander.net/
Work: http://www.redpill-linpro.com/