how to fix,"Call to a member function row() on null " - codeigniter

Question

How to fix
Call to a member function row() on null
THIS IS MY CONTROLLER
function forwardtrack($param='',$param2='') {
if(sizeof($this->db->get_where('st_forward',array('letter_no' =>$param.'/'.$param2))->result_array())>0 && (!($param.'/'.$param2) )){
$data1['message']= 'notallow';
$this->load->view('track1',$data1);
}
else{
$data1['name']=$this->db->get_where('bpas_user_profiles',array('AgencyMainParentID' =>$this->session->userdata('ministryId'),'AgencyParentID'=>$this->session->userdata('parentID'),'AgencyID'=>$this->session->userdata('agencyID')))->result_array();
$data1['userdeatils']=$this->ag->tracks($param.'/'.$param2);
$this->load->view('userManagement/forward2', $data1);
}
/* ag=> agency model */
}
THIS IS MY MODEL
public function tracks($letterno="")
{
$query= $this->db->get_where('st_dak_details',array('dakLetterNo'=>$letterno))->row();
return $query;
}
THIS VIEW PAGE
<br/>
<div class="container">
<div class="panel panel-info">
<div class="panel-heading">
<i class="fa fa-envelope-o fa-fw"></i>forward to
</div>
<div class="panel-body">
<form class="form-horizontal" enctype="multipart/form-data" action="#" method="post" id="forwardmessage">
<div class="form-group">
<label for="letter"class="col-xs-12 col-lg-1 col-sm-1 col-md-1">letter_no: </label>
<div class="input-group">
<span class="input-group-addon"><i class="glyphicon glyphicon-credit-card"></i></span>
<?php
foreach($userdeatils->row() as $row): ?>
<input name="dakLetterNo" id="dakLetterNo" value="<?php echo $row['dakLetterNo'];?>"readonly="true" class="form-control" type="text" required />
</div>
</div>
<!-- <div class="form-group">
<label class="col-xs-12 col-lg-2 col-sm-2 col-md-2">created: </label>
<div class="input-group">
<span class="input-group-addon"><i class="glyphicon glyphicon-credit-card"></i></span>
<input name="copy_to" id="copy_to" value="<?php //echo $userdeatils->created;?>"readonly="true" class="form-control" type="text" required />
</div> -->
<div class="form-group">
<label class="col-xs-12 col-lg-2 col-sm-2 col-md-2 control-label">Attachment: </label>
<div class="col-xs-12 col-lg-10 col-sm-10 col-md-10">
<input type="file" name="Attachment" id="Attachment">
</div>
</div>
<div class="form-group">
<label class="col-xs-12 col-lg-2 col-sm-2 col-md-2">Subject: </label>
<div class="input-group" class="col-xs-12 col-lg-10 col-sm-10 col-md-10">
<span class="input-group-addon" id="subjecterr"><i class="glyphicon glyphicon-credit-card"></i></span>
<input name="subject" id="Remark" value="<?php echo $row['Remark'];?>"readonly="true" class="form-control" type="text" required />
</div>
</div>
<div class="form-group">
<label class="col-xs-12 col-lg-2 col-sm-2 col-md-2">Place: </label>
<div class="input-group" class="col-xs-12 col-lg-10 col-sm-10 col-md-10">
<span class="input-group-addon"><i class="glyphicon glyphicon-credit-card"></i></span>
<input name="place" id="place" value="<?php echo $row['place'];?>"readonly="true" class="form-control" type="text" required />
</div>
</div>
<div class="form-group">
<label class="col-xs-12 col-lg-2 col-sm-2 col-md-2">from: </label>
<div class="input-group" class="col-xs-12 col-lg-10 col-sm-10 col-md-10">
<span class="input-group-addon"><i class="glyphicon glyphicon-credit-card"></i></span>
<input name="from" id="receieve_add" value="<?php echo $row['receieve_add'];?>"readonly="true" class="form-control" type="text" required />
</div>
</div>
<div class="form-group">
<label class="col-xs-12 col-lg-2 col-sm-2 col-md-2">Created: </label>
<div class="input-group" class="col-xs-12 col-lg-10 col-sm-10 col-md-10">
<span class="input-group-addon"><i class="glyphicon glyphicon-credit-card"></i></span>
<input name="created" id="created" value="<?php echo $row['created'];?>"readonly="true" class="form-control" type="text" required />
</div>
</div>
<!-- </div> -->
<!-- <div class="form-group"> -->
<!-- <label class="col-xs-12 col-lg-2 col-sm-2 col-md-2">Message: </label> -->
<!-- <div class="input-group" class="col-xs-12 col-lg-10 col-sm-10 col-md-10"> -->
<!-- <span class="input-group-addon"><i class="glyphicon glyphicon-credit-card"></i></span> -->
<!-- <input name="message" id="message" value="<?php //echo $userdeatils->created;?>"readonly="true" class="form-control" type="text" required /> -->
<!-- </div> -->
<!-- </div> -->
<?php endforeach;?>
<div class="form-group">
<label class="col-lg-2 col-xs-12 col-sm-2 col-md-2">Message: </label>
<div class="col-xs-12 col-lg-10 col-sm-10 col-md-10">
<textarea class="form-control" id="message" name="message"></textarea>
<span id="messageerr" class="text-danger"></span>
</div>
</div>
<div class="form-group">
<label class="col-lg-2 col-xs-12 col-sm-2 col-md-2">
Forward to
</label>
<div class="col-lg-6 col-xs-12 col-sm-6 col-md-6">
<select name="forwardto[]" id="agency" class="form-control">
<option value="">Select</option>
<?php
foreach($name as $row): ?>
<option value="<?php echo $row['cid']?>">
<?php echo $row['FirstName'].$row['MiddleName'].$row['LastName']?>
</option>
<?php endforeach;?>
</select>
<span id="forwarderr" class="text-danger"></span>
</div>

Answer 1

Model:
public function tracks($letterno="")
{
$query= $this->db->get_where('st_dak_details',array('dakLetterNo'=>$letterno));
if ($query->num_rows() > 0) {
return $query->row();
} else {
return array();
}
}
Controller:
function forwardtrack($param = '', $param2 = '') {
if (sizeof($this->db->get_where('st_forward', array('letter_no' => $param . '/' . $param2))->result_array()) > 0 && (!($param . '/' . $param2) )) {
$data1['message'] = 'notallow';
$this->load->view('track1', $data1);
} else {
$data1['name'] = $this->db->get_where('bpas_user_profiles', array('AgencyMainParentID' => $this->session->userdata('ministryId'), 'AgencyParentID' => $this->session->userdata('parentID'), 'AgencyID' => $this->session->userdata('agencyID')))->result_array();
$data1['userdeatils'] = $this->ag->tracks($param . '/' . $param2);
$this->load->view('userManagement/forward2', $data1);
}
/* ag=> agency model */
}
View:
<?php
if(!empty($userdeatils)){
foreach($userdeatils as $row) { ?>
//yout html code
...
...
<?php } ?>//foreach close
<?php } ?>//if close