For the page object of the snippet Generator a unique id or name for the 'select' Element for the tool selection is required. (cf. attached screenshot)
The item can not be identified by class name cause 'setting-input dropdownList' is not unique.
Seems that adding an ID is not so easy for those select controls.
I solved this problem in a general way now by adding the dependency to the [Form Element Path Plugin||https://wiki.jenkins.io/display/JENKINS/Form+Element+Path+Plugin].