adding watermark with typoscript does not work

[EnzephaloN]

Hello

I tried to add watermarks to the medium-images with this code
`
plugin.tx_yag.settings.themes{
mt2 < plugin.tx_yag.settings.themes.lightbox
mt2{
title = 'MyTheme2'
description = 'neues von Lightbox abgeleitetet Theme'

    showBreadcrumbs = 1

    itemList.itemsPerPage = 15
    itemList.columnCount = 5        

    resolutionConfigs {

        # Auf dem Bild das Wasserzeichen ausgeben.
        medium >
        medium = GIFBUILDER
        medium {
            XY = [10.w],[10.h]

            format = jpg
            quality = 90

            10 = IMAGE
            10 {
              file.maxH = 1200
              file.maxW = 1200
              file.import.field = yagImage
            }

            20 = IMAGE
            20 {
                file = EXT:theme_mt/Resources/Public/Images/mt-logo.png
                file.width = 120
                offset = [10.w]-180,[10.h]-70
            }                         
        }
    }                          
}    

}
`

But after choosing the template mt I get the error:

Fatal error: Call to a member function getForLocalProcessing() on null in /is/htdocs/www/site/typo3conf/ext/yag/Classes/Domain/ImageProcessing/Typo3Processor.php on line 86

I'm using TYPO3 7.6.21

[dominikmuellerwf]

Same problem here...