Validation Not working?

This simply says hey if there has been text input then update but if not then pull from previously set option right?

// validate our options
function plugin_options_validate($input) {
$options = get_option('plugin_options');

  if(strlen($options['text_string']) > 0){
	  $options['text_string'] = trim($input['text_string']);
  }elseif(!strlen($options['text_string']) > 0){
	  $options['text_string'] = $options['text_string'];
  }
return $options;
}