This feature is available in all editions.
My report has rows with data, but why is the associated work item blank?
Blank rows may occur if the associated work items have been deleted. Try checking your recycle bin to see if the item is there. You also use Advanced Search, and select the Deleted check box to display the items that have been deleted.
When a work item is deleted, the Effort associated with that work item is NOT deleted. Although Effort cannot be removed, you can negate it by adding a negative value such that the sum of effort for the work item is zero (0).