PaletteManipulator causes error, if palette happens to have 'invalid' data

[fritzmg]

Affected version(s)
4.7.2

Description
If a palette contains a trailing ; for example and you try to apply anything on that palette with the PaletteManipulator the following error will occur:

TypeError:
preg_match() expects parameter 2 to be string, null given

  at vendor/contao/contao/core-bundle/src/DataContainer/PaletteManipulator.php:199
  at preg_match('#\\{(.+?)(:hide)?\\}#', null, array('{invisible_legend:hide}', 'invisible_legend', ':hide'))
     (vendor/contao/contao/core-bundle/src/DataContainer/PaletteManipulator.php:199)
  at Contao\CoreBundle\DataContainer\PaletteManipulator->explode('{type_legend},type,headline;{template_legend:hide},customTpl;{protected_legend:hide},protected;{expert_legend:hide},guests,cssID;{invisible_legend:hide},invisible,start,stop;')
     (vendor/contao/contao/core-bundle/src/DataContainer/PaletteManipulator.php:139)
  at Contao\CoreBundle\DataContainer\PaletteManipulator->applyToString('{type_legend},type,headline;{template_legend:hide},customTpl;{protected_legend:hide},protected;{expert_legend:hide},guests,cssID;{invisible_legend:hide},invisible,start,stop;')
     (vendor/contao/contao/core-bundle/src/DataContainer/PaletteManipulator.php:119)
  at Contao\CoreBundle\DataContainer\PaletteManipulator->applyToPalette('headline', 'tl_content')
     (app/Resources/contao/dca/tl_content.php:8)
  at include('…/app/Resources/contao/dca/tl_content.php')
     (vendor/contao/contao/core-bundle/src/Resources/contao/library/Contao/DcaLoader.php:94)
  at Contao\DcaLoader->load(false)
     (vendor/contao/contao/core-bundle/src/Resources/contao/library/Contao/Controller.php:1279)
  at Contao\Controller::loadDataContainer('tl_content')
     (vendor/contao/contao/core-bundle/src/Resources/contao/drivers/DC_Table.php:3391)
  at Contao\DC_Table->reviseTable()
     (vendor/contao/contao/core-bundle/src/Resources/contao/drivers/DC_Table.php:319)
  at Contao\DC_Table->showAll()
     (vendor/contao/contao/core-bundle/src/Resources/contao/classes/Backend.php:616)
  at Contao\Backend->getBackendModule('article', null)
     (vendor/contao/contao/core-bundle/src/Resources/contao/controllers/BackendMain.php:169)
  at Contao\BackendMain->run()
     (vendor/contao/contao/core-bundle/src/Controller/BackendController.php:48)
  at Contao\CoreBundle\Controller\BackendController->mainAction()
     (vendor/symfony/http-kernel/HttpKernel.php:150)
  at Symfony\Component\HttpKernel\HttpKernel->handleRaw(object(Request), 1)
     (vendor/symfony/http-kernel/HttpKernel.php:67)
  at Symfony\Component\HttpKernel\HttpKernel->handle(object(Request), 1, true)
     (vendor/symfony/http-kernel/Kernel.php:198)
  at Symfony\Component\HttpKernel\Kernel->handle(object(Request))
     (web/app_dev.php:83)

This is a problem, because some extensions aren't very "clean" when it comes to palette manipulation. A trailing ; that was added by one extension should not break the usage of the PaletteManipulator of any following extension.

How to reproduce
Create the file app/Resources/contao/dca/tl_content.php with the following content:

<?php

$GLOBALS['TL_DCA']['tl_content']['palettes']['headline'] .= ';';

\Contao\CoreBundle\DataContainer\PaletteManipulator::create()
    ->addLegend('test_legend', 'expert_legend')
    ->addField('testField', 'test_legend')
    ->applyToPalette('headline', 'tl_content');

Then log into the back end and go to Content » Articles. The aforementioned error will occur.

[leofeyer]

Fixed in 02fa1e1.