Place custom Block, return Internal Server Error I create a Block Plugin in a module,
it be showing the available blocks but when I try to place the block, it returns in the browser console the follow error:


  AjaxError: 
  An AJAX HTTP error occurred.
  HTTP-resultaatcode: 500
  Debug informatie volgt.
  Pad: /admin/structure/block/add/hello_block/bartik?region=footer_fourth
  Statustekst: Internal Server Error
  Antwoordtekst: 


I have place the code on the follow place:
DrupalRoot/modules/pagebuilder/src/Plugin/Block/testblock.php

&lt;?php

/**
 * @file
 * Contains \Drupal\pagebuilder\Plugin\Block\testblock.
 */
namespace Drupal\pagebuilder\Plugin\Block
use Drupal\Core\Block\BlockBase;

/**
 * Provides a 'Hello' Block
 *
 * @Block(
 *   id = "hello_block",
 *   admin_label = @Translation("Hello block"),
 * )
 */
class testblock extends BlockBase {

    /**
     * {@inheritdoc}
     */
    public function build() {
        return array(
            '#markup' =&gt; $this-&gt;t('Hello, World!'), 
        );
    }
}
?&gt;


How can i fix this problem?
When developing and encounter 500 errors, you should see if Drupal has logged the error or your webserver has logged the error. Depending on your configuration you might be able to see a full stacktrace explaining the error.

In this case you are missing a ; after your namespace declaration. So

namespace Drupal\pagebuilder\Plugin\Block

Should be

namespace Drupal\pagebuilder\Plugin\Block;

This should fix your error.