Setting a default value on settings form return null in Octobercms

I create a little plugin for the OctoberCMS but now dealing with a problem of setting a default value for a settings form.

I used database storage for my plugin settings (Backend -> Settings tab -> My Plugin tab) which works , quite good, except I caot set default values.

I have a fields.yaml with this content:

tabs:
    fields:
        reviews_border_color:
            label: 'Field1'
            span: left
            tab: 'review_sticker'
            required: 1
            type: text
            default: '#F2F2F2'
        rating_star_size:
            label: 'Field2'
            span: left
            tab: 'review_sticker'
            required: 1
            type: number
            default: 14

I retrieve the settings in my components like this:

<?php namespace CodedgeTestPluginComponents;

use CmsClassesComponentBase;
use CodedgeTestPluginModelsSettings;

class TestComponent extends ComponentBase
{
    public $starSize;
    public $borderColor;

    public function componentDetails()
    {
        retu [
            'name'        => 'Test Component',
            'description' => '...'
        ];
    }

    public function defineProperties()
    {
        retu [];
    }

    public function init()
    {
        $this->starSize = Settings::get('rating_star_size'); // not giving a default value when empty, default is 14
        $this->borderColor = Settings::get('reviews_border_color'); // not giving a default value when empty, default is '#F2F2F2'
    }

}

I also tried to set the default value as second param in the get() method, like this:

public function init()
{
    $this->starSize = Settings::get('rating_star_size', 14); // retus null
    $this->borderColor = Settings::get('reviews_border_color', '#F2F2F2'); // retus null
}

So any suggestions how I can reliably set a default value if none is specified/entered in to the settings form field?