Issue #2827097 by pfrenssen: $plugin_id is a string, not an array

core/lib/Drupal/Core/Field/WidgetBase.php

@@ -36,7 +36,7 @@ abstract class WidgetBase extends PluginSettingsBase implements WidgetInterface
   /**
    * Constructs a WidgetBase object.
    *
-   * @param array $plugin_id
+   * @param string $plugin_id
    *   The plugin_id for the widget.
    * @param mixed $plugin_definition
    *   The plugin implementation definition.