mysql - Syntax error or access violation php sql

i have added this sql in my code ,

function devenir_client_dataforform() {
        $type = $_POST['clientType'];
        //$produitname = $_POST['produitname'];
        $produitnid = $_POST['produitnid'];
        $query = db_select('node', 'n');

        $query->leftjoin('field_data_field_description_col_1', 'img', 'img.entity_id = n.nid');
        $query->leftjoin('field_data_field_pdf_file_image', 'pdf', 'pdf.entity_id = n.nid');

        $query->leftjoin('taxonomy_term_data', 't', 't.tid ='.$type); 



        $query->condition('n.nid', $produitnid, '=')
              //->condition('t.tid', $type, '=')
              ->fields('n', array('title'))
              ->fields('t', array('name'))
              ->fields('pdf', array('field_pdf_file_image_fid'))
              ->fields('img', array('field_description_col_1_value'));


        $result = $query->execute();
        foreach ($result as $record) {
            if(!empty($record->field_description_col_1_value)) {
                $fid =  $record->field_description_col_1_value;
                $produitname =  $record->title;
                $pdf =  $record->field_pdf_file_image_fid;
                $tp = $record->name;

            }

        }   
        $file = file_load($pdf);
        $uri = $file->uri;

        $path = file_create_url($uri);
        //$uri = image_style_path( $path);
         $items[] =  array(
                            "type" => $tp ,
                            "produitname" => $produitname,
                            "produitnid" => $produitnid,

                            "image" => $fid,
                            "pdf" => $path,
                            "typeid" => $type
                    );
        return $items;
    }

but in the last step there is an error

PDOException: SQLSTATE[42000]: Syntax error or access violation: 1064
You have an error in your SQL syntax; check the manual that
corresponds to your MySQL server version for the right syntax to use
near 'WHERE (n.nid = NULL)' at line 4: SELECT n.title AS title, t.name
AS name, pdf.field_pdf_file_image_fid AS field_pdf_file_image_fid,
img.field_description_col_1_value AS field_description_col_1_value
FROM {node} n LEFT OUTER JOIN {field_data_field_description_col_1} img
ON img.entity_id = n.nid LEFT OUTER JOIN
{field_data_field_pdf_file_image} pdf ON pdf.entity_id = n.nid LEFT

OUTER JOIN {taxonomy_term_data} t ON t.tid = WHERE (n.nid =
:db_condition_placeholder_0) ; Array ( [:db_condition_placeholder_0]
=> ) in devenir_client_dataforform() (line 189 of /home/dotit_bh/bh-website.dotit.mobi/sites/all/modules/devenir_client/devenir_client.module).

Answer

Error in this part of SQL Query:

 WHERE (n.nid = NULL)

Correct SQL Query:

WHERE (n.nid is NULL)

You shall rewrite your script:

$nid_operator = ($produitnid ? '=' : 'is');

$query->condition('n.nid', $produitnid, $nid_operator)
              //->condition('t.tid', $type, '=')
              ->fields('n', array('title'))
              ->fields('t', array('name'))
              ->fields('pdf', array('field_pdf_file_image_fid'))
              ->fields('img', array('field_description_col_1_value'));