Error on editing categories in Magento 2

Question

I've inherited a Magento 2 site and am getting an error when trying to save changes in the dashboard to categories "There has been an error processing your request"

Is the below a theme compatibility error? - we've just updated the site to 2.1.8.

The log for the errors looks like - any pointers much appreciated:

a:4:{i:0;s:349:"Warning: Declaration of Plazathemes\Override\Controller\Adminhtml\Category\Save::imagePreprocessing($data) should be compatible with Magento\Catalog\Controller\Adminhtml\Category\Save::imagePreprocessing(array $data) in /srv/users/serverpilot/apps/red-hot-racing/public/app/code/Plazathemes/Override/Controller/Adminhtml/Category/Save.php on line 82";i:1;s:4499:"#0 /srv/users/serverpilot/apps/red-hot-racing/public/vendor/composer/ClassLoader.php(444): Magento\Framework\App\ErrorHandler->handler(2, 'Declaration of ...', '/srv/users/serv...', 82, Array)
#1 /srv/users/serverpilot/apps/red-hot-racing/public/vendor/composer/ClassLoader.php(444): include()
#2 /srv/users/serverpilot/apps/red-hot-racing/public/vendor/composer/ClassLoader.php(322): Composer\Autoload\includeFile('/srv/users/serv...')
#3 [internal function]: Composer\Autoload\ClassLoader->loadClass('Plazathemes\\Ove...')
#4 [internal function]: spl_autoload_call('Plazathemes\\Ove...')
#5 /srv/users/serverpilot/apps/red-hot-racing/public/vendor/magento/framework/ObjectManager/Relations/Runtime.php(38): class_exists('Plazathemes\\Ove...')
#6 /srv/users/serverpilot/apps/red-hot-racing/public/vendor/magento/framework/Interception/Config/Config.php(153): Magento\Framework\ObjectManager\Relations\Runtime->has('Plazathemes\\Ove...')
#7 /srv/users/serverpilot/apps/red-hot-racing/public/vendor/magento/framework/Interception/Config/Config.php(176): Magento\Framework\Interception\Config\Config->_inheritInterception('Plazathemes\\Ove...')
#8 /srv/users/serverpilot/apps/red-hot-racing/public/vendor/magento/framework/Interception/ObjectManager/Config/Developer.php(61): Magento\Framework\Interception\Config\Config->hasPlugins('Plazathemes\\Ove...')
#9 /srv/users/serverpilot/apps/red-hot-racing/public/vendor/magento/framework/ObjectManager/Factory/Dynamic/Developer.php(70): Magento\Framework\Interception\ObjectManager\Config\Developer->getInstanceType('Plazathemes\\Ove...')
#10 /srv/users/serverpilot/apps/red-hot-racing/public/vendor/magento/framework/ObjectManager/ObjectManager.php(57): Magento\Framework\ObjectManager\Factory\Dynamic\Developer->create('Plazathemes\\Ove...', Array)
#11 /srv/users/serverpilot/apps/red-hot-racing/public/vendor/magento/framework/App/ActionFactory.php(40): Magento\Framework\ObjectManager\ObjectManager->create('Magento\\Catalog...')
#12 /srv/users/serverpilot/apps/red-hot-racing/public/vendor/magento/framework/App/Router/Base.php(300): Magento\Framework\App\ActionFactory->create('Magento\\Catalog...')
#13 /srv/users/serverpilot/apps/red-hot-racing/public/vendor/magento/framework/App/Router/Base.php(161): Magento\Framework\App\Router\Base->matchAction(Object(Magento\Framework\App\Request\Http), Array)
#14 /srv/users/serverpilot/apps/red-hot-racing/public/vendor/magento/framework/App/FrontController.php(50): Magento\Framework\App\Router\Base->match(Object(Magento\Framework\App\Request\Http))
#15 /srv/users/serverpilot/apps/red-hot-racing/public/vendor/magento/framework/Interception/Interceptor.php(74): Magento\Framework\App\FrontController->dispatch(Object(Magento\Framework\App\Request\Http))
#16 /srv/users/serverpilot/apps/red-hot-racing/public/vendor/magento/framework/Interception/Chain/Chain.php(70): Magento\Framework\App\FrontController\Interceptor->___callParent('dispatch', Array)
#17 /srv/users/serverpilot/apps/red-hot-racing/public/vendor/magento/framework/Interception/Interceptor.php(138): Magento\Framework\Interception\Chain\Chain->invokeNext('Magento\\Framewo...', 'dispatch', Object(Magento\Framework\App\FrontController\Interceptor), Array, 'install')
#18 /srv/users/serverpilot/apps/red-hot-racing/public/vendor/magento/framework/Module/Plugin/DbStatusValidator.php(69): Magento\Framework\App\FrontController\Interceptor->Magento\Framework\Interception\{closure}(Object(Magento\Framework\App\Request\Http))
#19 /srv/users/serverpilot/apps/red-hot-racing/public/vendor/magento/framework/Interception/Interceptor.php(142): Magento\Framework\Module\Plugin\DbStatusValidator->aroundDispatch(Object(Magento\Framework\App\FrontController\Interceptor), Object(Closure), Object(Magento\Framework\App\Request\Http))
#20 /srv/users/serverpilot/apps/red-hot-racing/public/var/generation/Magento/Framework/App/FrontController/Interceptor.php(26): Magento\Framework\App\FrontController\Interceptor->___callPlugins('dispatch', Array, Array)
#21 /srv/users/serverpilot/apps/red-hot-racing/public/vendor/magento/framework/App/Http.php(135): Magento\Framework\App\FrontController\Interceptor->dispatch(Object(Magento\Framework\App\Request\Http))
#22 /srv/users/serverpilot/apps/red-hot-racing/public/vendor/magento/framework/App/Bootstrap.php(258): Magento\Framework\App\Http->launch()
#23 /srv/users/serverpilot/apps/red-hot-racing/public/index.php(39): Magento\Framework\App\Bootstrap->run(Object(Magento\Framework\App\Http))
#24 {main}";s:3:"url";s:103:"/backoffice/catalog/category/save/key/20527759d571e013532febbcc8fc34bcbca874ffcae29f96e4901cb74fd78569/";s:11:"script_name";s:10:"/index.php";}

The method referenced in the error above:

 /**
     * Image data preprocessing
     *
     * @param array $data
     *
     * @return array
     */
    public function imagePreprocessing($data)
    {
        if (empty($data['image'])) {
            unset($data['image']);
            $data['image']['delete'] = true;
        }

        if (empty($data['thumb_nail'])) {
            unset($data['thumb_nail']);
            $data['thumb_nail']['delete'] = true;
        }

        return $data;
    }

Answer 1

Replace imagePreprocessing by following code:

/**
 * Image data preprocessing
 *
 * @param array $data
 *
 * @return array
 */
public function imagePreprocessing(array $data)
{
    if (empty($data['image'])) {
        unset($data['image']);
        $data['image']['delete'] = true;
    }

    if (empty($data['thumb_nail'])) {
        unset($data['thumb_nail']);
        $data['thumb_nail']['delete'] = true;
    }

    return $data;
}