A error creating filter - filter tips I want to create a filter text module for drupal 8.

emtfilter/src/Plugin/Filter/emtfilter.php



/**
 * @file
 * Contains \Drupal\emtfilter\Plugin\Filter\emtfilter.
 */

namespace Drupal\emtfilter\Plugin\Filter;

use Drupal\Core\Form\FormStateInterface;
use Drupal\filter\FilterProcessResult;
use Drupal\filter\Plugin\FilterBase;

/**
 * Text filter for highlighting PHP source code.
 *
 * @Filter(
 *   id = "emtfilter",
 *   module = "emtfilter",
 *   title = @Translation("Tipograf"),
 *   description = @Translation("Tipograf"),
 *   type = Drupal\filter\Plugin\FilterInterface::TYPE_HTML_RESTRICTOR,
 * )
 */
class emtfilter extends FilterBase { 


  /**
   * {@inheritdoc}
   */
  public function tips($long = FALSE) {
    if ($long) {
      return t('text1r-');
    }
    else {
      return t('text2r-');
    }
  }

  /**
   * {@inheritdoc}
   */
  public function process($text, $langcode) {
        return new FilterProcessResult($text);
  }    
}


After clearing cashe everything is ok. But when I visit some forms with textfields second time, Drupal generates this error:


  Notice: _filter_tips(): The script tried to execute a method or access a property of an incomplete object. Please ensure that the class definition "Drupal\emtfilter\Plugin\Filter\emtfilter" of the object you are trying to operate on was loaded before unserialize() gets called or provide a __autoload() function to load the class definition in _filter_tips() (line 350 of core/modules/filter/filter.module).
  _filter_tips('full_html', ) (Line: 378)
  template_preprocess_filter_guidelines(Array, 'filter_guidelines', Array) (Line: 293)


And my tips disappear. What am I do wrong?
I made a mistake in the letter case in the class file (emtFilter.php -> emtfilter.php)