Inventory Import API should not fail if targetFolder is "/"

Current Situation

When executing an Inventory import it is possible to set the target folder. The import will create this folder and store all items with this folder as the parent.

When the foldername is / a NPE occurs.

Desired Behavior

When executing an Inventory import, the empty value for the target folder and the value / should be handled in the same way without throwing a NPE.