Value duplication when importing file . csv when one or more column(s) is missing from the file

Question

When I import a . csv file to save to the database and the file is missing the name of some column instead of inserting null in the bank it repeats the value of the first column.

Following example;

$sourcePath = $_FILES['fileTabelaTeste']['tmp_name'];
$targetPath = "/pages/dados/".$_FILES['fileTabelaTeste']['name'];

move_uploaded_file($sourcePath,$targetPath);
$abraArq = fopen("/pages/dados/".$_FILES['fileTabelaTeste']['name']."","r");


    $fieldnames = fgetcsv($abraArq, 5000, ',');

    $idx_prod_codigo = array_search("prod_codigo", $fieldnames);
    $idx_prod_descricao = array_search("prod_descricao", $fieldnames);
    $idx_prod_site = array_search("prod_site", $fieldnames);
    $idx_prod_peso_bruto = array_search("prod_peso_bruto", $fieldnames);
    $idx_und_codigo = array_search("und_codigo", $fieldnames);

    while ($row = fgetcsv($abraArq , 4096, ',')) {
        $prod_codigo = $row[$idx_prod_codigo];
        $prod_descricao = $row[$idx_prod_descricao];
        $prod_site = $row[$idx_prod_site];          
        $prod_peso_bruto = $row[$idx_prod_peso_bruto];
        $prod_peso_bruto = str_replace(",",".",$prod_peso_bruto);
        $und_codigo = $row[$idx_und_codigo];

     $insert = mysql_query("INSERT INTO produtosTeste

                (PROD_CODIGO, PROD_DESCRICAO, PROD_SITE, PROD_PESO_BRUTO, UND_CODIGO) values

                ('$prod_codigo','$prod_descricao','$prod_site','$prod_peso_bruto','$und_codigo') ") or die(mysql_error());
     }

the csv file comes by an input file, and if in this file, for example, you do not have the und_code column, you enter the same value as the prod_code.

Inside the while after assigning the value to the variable $pro_codigo assigns null to the $row[$idx_prod_codigo], which was the value that was going to the columns that were supposed to save null, and solved temporarily.