*PatternLab* PHP Warning: htmlspecialchars() expects parameter 1 to be string

i have a big Project using PatternLab and Mustache. Everytime i start my Patternlab the Error

PHP Warning: htmlspecialchars() expects parameter 1 to be string, array given 
in ../../../core/lib/MUstache/Engine.php(583) : eval()'d code on line 29

occurs about 30 or 40 times. I found already that it may be a Mustache-Variable that is not defined in the JSON-File. But since the Project is so big and im new to it i can't figure out what Variable in what File is undefined.

My Question: Is there any way to find this Variable that is not defined?

Thanks for all Answers from you Guys!