Problem

The termcollection create method return type is changed and there are one missing reference which uses the old return type.

The reference can be found in:

editor_Plugins_TermImport_Services_Import::handleCollectionForFile

Change the 

//create new term collection/language resource
$collectionId=$model->create($collectionName, [$customerId]);

to

//create new term collection/language resource
$collectionId=$model->create($collectionName, [$customerId])->getId();

Additional:

Double check if there are other references to this function!