json gere les champs null

j'ai un fichier json je voudrais gerer le champs null

$date = date("dmY");
$saut = "\n";

// chemin du fichier json programme
$json = file_get_contents("https://offline.turfinfo.api.pmu.fr/rest/client/7/programme/$date");
$data = json_decode($json,true);
$nb = count($data ['programme'] ['reunions']);
//$nc = count($data ['programme'] ['reunions']['courses']);
for($i = 0  ; $i < $nb ; $i ++){

$reunion         = $data ['programme'] ['reunions'][$i]['courses'] ;
//$nc              = $data ['programme'] ['reunions'][$i]['courses'][$i] ;

$reuni  = $i+1;
$course = $i+1;
var_dump($course);
echo 'R'.$reuni ;  
    foreach ($reunion as $r){

echo "<br>".$r ['cached'], " "
           .$r ['departImminent'], " "
           .$r ['timezoneOffset']," "
           .$r ['numReunion']
           .$r ['numOrdre']," "
           .$r ['numExterne']," "
           .$r ['heureDepart']," "
           .$r ['libelle'], " "
           .$r ['libelleCourt'], " "
           .$r ['montantPrix']," "
           .$r ['parcours']," "
           .$r ['distance']," "
           .$r ['distanceUnit']," "
           .$r ['corde']," "
           .$r ['discipline']," "
           .$r ['specialite']," "
           .$r ['categorieParticularite']," "
           .$r ['conditionSexe']," "
           .$r ['nombreDeclaresPartants']," "
           .$r ['grandPrixNationalTrot']," "
           .$r ['numSocieteMere']," "
           .$r ['pariMultiCourses']," "
           .$r ['pariSpecial']," "
           .$r ['montantTotalOffert']," "
           .$r ['montantOffert1er']," "
           .$r ['montantOffert2eme']," "
           .$r ['montantOffert3eme']," "
           .$r ['montantOffert4eme']," "
           .$r ['montantOffert5eme']," "
           // paris
           // fin paris
           .$r ['statut']," "
           .$r ['categorieStatut']," "
          // .$r ['participants']," "
          // .$r ['ecuries']," "
           .$r ['rapportsDefinitifsDisponibles']," "
           .$r ['isDepartImminent']," "
           .$r ['isDepartAJPlusUn']," "
           //.$r ['cagnottes']," "
          // .$r ['cagnottes']," "
           .$r ['replayDisponible']," "
           // hippodrome
           //.$r['code']," "
           //.$r['libelleCourt']," "
           //.$r['libelleLong']," "
           //fin hippodrome
           .$r ['epcPourTousParis']," "
           .$r ['courseTrackee']," "
           .$r ['courseExclusiveInternet']," "
           .$r ['formuleChampLibreIndisponible']," "
           .$r ['hasEParis'];
           //date Programme
           //.$r [''];
echo  "<br>". $saut;
    }
     }ourez votre code en utilisant "```" pour bien le mettre en forme. (ne copier pas trop de code)

Ce que je veux
je voudrai gerer les champs vide pour evidtez les erreur
et je voudrai rajouter une variable pour chaque course pour les reunion sa marche mais ma pour les course
je voudrais obtenir R1C1
j'ai essayer avec un (isset(.$r ['corde'])," " mais sa ne fonctionne pas
merci d'avance

Ce que j'obtiens
Notice: Undefined index: corde in C:\laragon\www\Pmu\reunion.php on line 41