Using $ this when not in an object context a call method inside a class

I have this line of code that calls buildField method from Field class name

$field_dictionary[$key] = Field::buildField($key, $request);

      

        
        
        
      

    

The Field class uses the buildField method here

public function buildField($key, $request) {

    $field_vocabulary = [];

    $image = $_FILES[$key];
    $image['tmp_name']['image'] = true;
    // Calling this another method from same class
    $field = $this->sanitizeFieldRows($image['tmp_name'], $request->post($key . '_name'), $request->post($key . '_description'));

    $field_vocabulary['name'] = implode('|', $field->field_1);
    $field_vocabulary['description'] = implode('|', $field->field_2);
    $field_vocabulary['image'] = implode('|', $field->reference);

    return $field_vocabulary;
}

      

        
        
        
      

    

This code has a line like this

$field = $this->sanitizeFieldRows($image['tmp_name'], $request->post($key . '_name'), $request->post($key . '_description'));

      

        
        
        
      

    

I am calling another method from the same class. It does some function that I just removed for so long.

public function sanitizeFieldRows($reference, $field_1, $field_2 = null) {

    // Some code etc.....
    // Outputs an object
    return (object) $output;
}

      

        
        
        
      

    

But the point is what I call $this->sanitizeFieldRows($par1,$par2,$par3)

, but it throws an error:

Using $this when not in object context in

      

        
        
        
      

    

But when I did Field::sanitizeFieldRows($par1,$par2,$par3)

, it works, but this method is in the same object, but it is not a static method that I am calling.

Is there something wrong with that?

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