我试图在codeigniter中为每个chkey获取一个数据，其中包含一个相关的值作为一个组。当有2个或更多的chkey时，则代码正常工作。但当只有一个chkey时，它会显示该chkey的值，但它会显示额外的值chkey:null,value:null in json。chkey的相关json为1，如下所示

[{"unit_id":"8","CHGRAPHUpdatetime":{"time":"2018-03-15 00:00:00,2018-03-15 00:00:00,2018-03-15 00:00:00,2018-03-15 00:00:00"},"channelGraph":[{"chkey":"ch1","list":"2,-30,12,20"},{"chkey":"null","list":"null"}]}]

预期是，

[{"unit_id":"8","CHGRAPHUpdatetime":{"time":"2018-03-15 00:00:00,2018-03-15 00:00:00,2018-03-15 00:00:00,2018-03-15 00:00:00"},"channelGraph":[{"chkey":"ch1","list":"2,-30,12,20"}]}]

你能帮我解决这个问题吗。
型号代码-

public function chGraph($unitid){
           $this->db->select("unit_id");
           $this->db->from("device_unit");
           $this->db->where('unit_id', $unitid);
           $query = $this->db->get();
           $unit = $query->result_array();
           $j = 0;
     foreach($unit as $row) {
         $unit[$j]['CHGRAPHUpdatetime'] = $this->UnitCHGRAPHUpdatetime($row['unit_id']);
           $unit[$j++]['channelGraph'] = $this->UnitCHGRAPHDetails1($row['unit_id']);

      }
      return $unit;
      }
        public function UnitCHGRAPHDetails1($unit_id)
    { 
        $this->db->select('distinct(chkey)','chvalue');
        $this->db->from('channel_info'); 
        $query = $this->db->get();
        $channelgraphData = $query->result_array();
        $m = 0;

      foreach($channelgraphData as $row) {
           $chvalueQuery = 'SELECT chkey, GROUP_CONCAT(chvalue)as list FROM channel_info where chkey= "'. $row['chkey'] .'"  and unit_id='. $unit_id .'';
           $response = $this->db->query($chvalueQuery)->row(); 
           $channelgraphData[$m++] = $response;
        }
        return $channelgraphData;
    }

控制器代码-

public function chGraph()
  {
     $unitid =  $this->uri->segment('3');
     $GraphDetails = $this->device_model->chGraph($unitid);
    echo json_encode($GraphDetails);
  }