Description:
------------
when you get data you assume NULL if dbdatlen == 0 however is possible that data is just an empty string (''), in this case you should check that dbdatlen == 0 and dbdata == NULL.

Reproduce code:
---------------
I use this test script (pwd.inc define just variable to connect)

<?php

// $Id: null.php,v 1.2 2006/10/20 14:38:22 freddy77 Exp $

require_once("pwd.inc");

$conn = mssql_connect($server,$user,$pass) or die("opps");

mssql_query("CREATE TABLE #MyTable (
   myfield VARCHAR(10) NULL,
   n INT
)", $conn) or die("error querying");


mssql_query("INSERT INTO #MyTable VALUES('',1)
INSERT INTO #MyTable VALUES(NULL,2)
INSERT INTO #MyTable VALUES(' ',3)
INSERT INTO #MyTable VALUES('a',4)", $conn) or die("error querying");

$result = 0;

function test($sql, $expected)
{
        global $conn, $result;

        $res = mssql_query($sql, $conn) or die("query");
        $row = mssql_fetch_assoc($res);
        $s = $row['myfield'];

        if (is_null($s))
                $s = '(NULL)';
        else if ($s == '')
                $s = '(Empty String)';
        else
                $s = "'".str_replace("'", "''", $s)."'";
        echo "$sql -> $s\n";
        if ($s != $expected)
        {
                echo "error!\n";
                $result = 1;
        }
}

test("SELECT top 1 * FROM #MyTable WHERE n = 1 -- ''", "(Empty String)");

test("SELECT top 1 * FROM #MyTable WHERE n = 2 -- NULL", "(NULL)");

test("SELECT top 1 * FROM #MyTable WHERE n = 3 -- ' '", "' '");

test("SELECT top 1 * FROM #MyTable WHERE n = 4 -- 'a'", "'a'");

exit($result);
?>


Expected result:
----------------
SELECT top 1 * FROM #MyTable WHERE n = 1 -- '' -> (Empty String)
SELECT top 1 * FROM #MyTable WHERE n = 2 -- NULL -> (NULL)
SELECT top 1 * FROM #MyTable WHERE n = 3 -- ' ' -> ' '
SELECT top 1 * FROM #MyTable WHERE n = 4 -- 'a' -> 'a'


Actual result:
--------------
SELECT top 1 * FROM #MyTable WHERE n = 1 -- '' -> (NULL)
error!
SELECT top 1 * FROM #MyTable WHERE n = 2 -- NULL -> (NULL)
SELECT top 1 * FROM #MyTable WHERE n = 3 -- ' ' -> ' '
SELECT top 1 * FROM #MyTable WHERE n = 4 -- 'a' -> 'a'