You can prevent the opening of an empty Tooltip by handling the loaded event of the content loading into the Tooltip template.
Step 1: Consider the TextBlock as the content of the Tooltip. In the following code example, the loaded event of the TextBlock is handled and the parent, Tooltip, is found by using the FindAncestor method. When the TextBlock.Text is empty, then set the ToolTip.IsOpen to false to prevent opening an empty Tooltip.
Step 2: The customized TextBlock is loaded into the Tooltip template of the GridColumn.ToolTipTemplate to achieve the desired result.
Note: You have to set the GridColumn.ShowToolTip to enable ToolTip support as given in the above code.
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