If condition check not working and execute even when the condition is false while doing post operation

Hello experts,

I am trying to check if the post data obtained for 'fields' is empty. I have tried different conditions to check if the array is empty or not. Even if the 'fields' is empty, the if condition executes. It would be great if someone could suggest me as to how to go about with this.

View:
<h4>Alternatives</h4><input type="text" style="width:700px;display: inline" id="fields" name="fields[]" placeholder="Enter Method Name" class="form-control method_list_list"/> <input type="button" name="addmore" id="addmore" class="btn btn-success" value="Add More"/>

Model:
public function addmethodtotask(){
	 $conn= mysqli_connect("localhost","root","","cognitivewalkthrough");
	 $taskid=  $_POST['taskid'];
	$description =  $_POST['reason'];
	$action = $_POST['action'];

//if (isset($_POST['fields']) && $_POST['fields'] != "") {
	if (isset($_POST['fields']) && $_POST['fields'] != NULL) {
	// if (count($_POST['fields'])>0 && !empty($_POST['fields'])) {
		 echo "whey am i here";
				foreach ( $_POST['fields'] as $key=>$value ) {
					$sql_website = sprintf("INSERT INTO method (methodname,description,action) VALUES ('%s','%s','%s')",mysqli_real_escape_string($conn,$value),mysqli_real_escape_string($conn,$description),mysqli_real_escape_string($conn,$action) );
					$this->db->query($sql_website);
					$inserted_method_id = $this->db->insert_id();
				}
	}
        $this->db->select('method.methodid,method.methodname,method.description,method.action,task.taskid,task.taskname');
	$this->db->from('method');
	$this->db->join('task_method', 'method.methodid = task_method.methodid');
	$this->db->join('task', 'task.taskid = task_method.taskid');
	$this->db->where('task_method.taskid',$taskid);
	$records = $this->db->get('');
	return $records->result();
}

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Thanks in advance.