redirect back withInput requries session otherwise old() empty

I am not sure if this is the correct behaviout.

In one of my controller methods -

PHP Code:

public function test() {
        $data_post = $this->request->getPost();
        if(!empty($data_post)) {
            $validation = $this->validate(
                ['what' => 'required',],
 ['what' => ['required'=>'Please enter what is required']]);

 if($validation == false) {
 redirect()->back()->withInput();
 exit;
            } else {
 //valid submission
 } 
 }
 
 $html = '<form method="post">
 <input type="text" class="form-control" name="what" id="what" value="'.old('what').'" />
 <button class="btn btn-success" type="submit">Submit</button>
 </form>';
 $html .= service('validation')->listErrors();

 echo view('myview', ['html' => $html]);
 
} 


It prints out the validation error message but old doesn't fill in the value in the input box.

However, if I just add

PHP Code:

session() 


in this code above it works fine.

Is this how it it is supposed to work? Or perhaps I need to make a session call in the constructor of the controller so that session is available in all the methods?