CVS NULL Documentation

Clearify documentation of CVS's output of NULL values, per suggestion
from Magnus.

Backpatch to 8.4.X.

doc/src/sgml/ref/copy.sgml

 <!--
-$PostgreSQL: pgsql/doc/src/sgml/ref/copy.sgml,v 1.87 2009/09/05 23:58:01 tgl Exp $
+$PostgreSQL: pgsql/doc/src/sgml/ref/copy.sgml,v 1.88 2009/09/17 21:13:01 momjian Exp $
 PostgreSQL documentation
 -->
 
@@ -550,12 +550,9 @@ COPY <replaceable class="parameter">count</replaceable>
    <para>
     The <literal>CSV</> format has no standard way to distinguish a
     <literal>NULL</> value from an empty string.
-    <productname>PostgreSQL</>'s <command>COPY</> handles this by
-    quoting. A <literal>NULL</> is output as the <literal>NULL</>
-    string and is not quoted, while a data value matching the
-    <literal>NULL</> string is quoted. Therefore, using the default
-    settings, a <literal>NULL</> is written as an unquoted empty
-    string, while an empty string is written with double quotes
+    <productname>PostgreSQL</>'s <command>COPY</> handles this using
+    quoting. A <literal>NULL</> is output as an empty string without
+    quotes, while an empty string data value is double-quoted
     (<literal>""</>).  Reading values follows similar rules. You can
     use <literal>FORCE NOT NULL</> to prevent <literal>NULL</> input
     comparisons for specific columns.