tooltip on datagrid error in log

We are using a (standard mendix) tooltip on our datagrid(s) and although the tooltip is working we get the following error in the log: Billing.Page.grid6: An error occurred in listener of event 'onRowMouseOver': TypeError: Cannot read property 'getGuid' of undefined Tooltip contents do not seem to matter. Tested in Chrome and Edge, no difference. Any thoughts? EDIT: Issue seems to disappear when switching off show empty rows. 
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