json_encode adding a null:null entry - php

Question

I have this code - it's not done by me :s and don't have time to replace the deprecated calls.
<?php
$mageFilename = 'app/Mage.php';
require_once $mageFilename;
umask(0);
Mage::app();
$db=mysql_connect('localhost','carros_mil1','K-Jw)ureB.}M');
mysql_select_db('carros_mil0',$db);
$nombreListModelo = 'modelo_'.str_replace(" ","_",strtolower($_REQUEST['nombreMarca']));
$sql = "SELECT DISTINCT (identificador) AS id
FROM modelos
WHERE nombre = '".$nombreListModelo."'";
$rs=mysql_query($sql);
$i=0;
while ($row = mysql_fetch_array($rs)) {
$vectorModelo[$i] = $row['id'];
$i++;
}
$sql = "SELECT attribute_id
FROM eav_attribute
WHERE attribute_code = '".$nombreListModelo."'";
$rs = mysql_query($sql);
$row = mysql_fetch_array($rs);
$id1 = $row['attribute_id'];
$sql= "SELECT eao.option_id AS option_id
FROM eav_attribute_option eao, eav_attribute_option_value eaov
WHERE eao.option_id=eaov.option_id AND attribute_id = ".$id1." ORDER BY eaov.value";
$rs=mysql_query($sql);
$retorno = array();
$bandera = true;
while ($row = mysql_fetch_array($rs)) {
$bandera = false;
$sql2= "SELECT value, option_id
FROM eav_attribute_option_value
WHERE option_id = ".$row['option_id']."
ORDER BY value";
$rs2=mysql_query($sql2);
$row2= mysql_fetch_array($rs2);
if ($_REQUEST['bandera']=='vende') {
if (!is_null($row2['value'])) $retorno[$row2['value']] = $row2['value'];
} else {
$existe=false;
for($k=0;$k<count($vectorModelo);$k++) {
if($row2['option_id'] == $vectorModelo[$k]) {
$existe=true;
break;
}
}
if($existe) {
if($_REQUEST['tipo']=='contactenos')
if (!is_null($row2['value'])) $retorno[$row2['value']] = $row2['value'];
else
if (!is_null($row2['option_id'])) $retorno[$row2['option_id']] = $row2['value'];
}
}
}
if($bandera)
$retorno[''] = 'Todos';
header('Content-Type: application/json');
//echo json_encode($retorno);
foreach($retorno as $k => $v) {
printf("%s => %s\n", $k, $v);
}
print_r($retorno);
echo json_encode($retorno);
Since I noticed something strange in the generated json, I added 2 different ways of printing the contents of the array.
The JSON way adds me a null:null entry. The strange case is that I'm checking !is_null($row2['value']) each time I add an element.
When I hit the url under certain parameters, I get:
Elantra => Elantra
Getz => Getz
H1 => H1
i-10 => i-10
New Accent => New Accent
Santa Fé => Santa Fé
Tucson => Tucson
Array
(
[Elantra] => Elantra
[Getz] => Getz
[H1] => H1
[i-10] => i-10
[New Accent] => New Accent
[Santa Fé] => Santa Fé
[Tucson] => Tucson
)
{"Elantra":"Elantra","Getz":"Getz","H1":"H1","i-10":"i-10","New Accent":"New Accent",null:null,"Tucson":"Tucson"}
The first 6 lines correspond to a custom print foreach loop. There's also a print_r call which only shows 6 elements. The 3rd form - which is the actual one I need - shows a null value.
So: Why is $retorno accepting null entries when I check the null condition beforehand? considering this script is full - no missing code here.

Answer 1

(Thanks #Hammerstein - don't know why you didn't write that as an answer).
The problem is that one of such values was not correctly being encoded, since it was not an ANSI value and was not encoded in UTF8. In this way, since "Santa Fé" had a "strange" character, it was encoded as null instead of "Santa F\u00e9".
Tip: Never assume your database is using an utf8_ charset
The solution was to explicitly encode the values when composing the array:
...
$bandera = false;
$sql2= "SELECT value, option_id
FROM eav_attribute_option_value
WHERE option_id = ".$row['option_id']."
ORDER BY value";
$rs2=mysql_query($sql2);
$row2= mysql_fetch_array($rs2);
//ENCODE the values to a good charset
$value = utf8_encode($row2['value']);
$option_id = utf8_encode($row['option_id'])
if ($_REQUEST['bandera']=='vende') {
$retorno[$value] = $value;
} else {
$existe=false;
for($k=0;$k<count($vectorModelo);$k++) {
if($row2['option_id'] == $vectorModelo[$k]) {
$existe=true;
break;
}
}
if($existe) {
if($_REQUEST['tipo']=='contactenos')
$retorno[$value] = $value;
else
$retorno[$option_id] = $value;
}
}
...