src/Core/Http/Serialization/JsonObjectSerializer.php
private function removeNullProperties($val){
        $filterArray = array_filter($val);
        $returned = array();
        foreach($filterArray as $k => $v){
          if(is_array($v)){
            if(FacadeHelper::isRecurrsiveArray($v)){
              $list = array();
              foreach($v as $kk => $vv){
                  $list[] = array_filter($vv);
              }
              $returned[$k] = $list;
            }
          }else{
            $returned[$k] = $v;
          }
        }
        return $returned;
    }
private function removeNullProperties($val){
        $filterArray = array_filter($val);
        $returned = array();
        foreach($filterArray as $k => $v){
          if(is_array($v)){
            if(FacadeHelper::isRecurrsiveArray($v)){
              $list = array();
              foreach($v as $kk => $vv){
                  $list[] = array_filter($vv);
              }
              $returned[$k] = $list;
            }
          }else{
            $returned[$k] = $v;
          }
        }
        return $returned;
    }
The input will always be an asscoiate array
So we will judge based on this two situration