code: private function _getSocialFallback ()
  	{
  		$image = null;
  
  		$assets = \Craft::$app->assets;
  
  		$fieldFallback = $this->_fieldSettings['socialImage'];
  
  		if (!empty($fieldFallback))
  			$image = $assets->getAssetById((int)$fieldFallback[0]);
  
  		else {
  			$seoFallback = $this->_seoSettings['socialImage'];
  
  			if (!empty($seoFallback))
  				$image = $assets->getAssetById((int)$seoFallback[0]);
  		}
  
  		return [
  			'title'       => $this->title,
  			'description' => $this->description,
  			'image'       => $image,
  		];
  	}
docs: Gets the social metadata fallback
  
  @return array