Hiding the collapse/expand mark when there is no data to be displayed by the toggle action target is not supported out of the box. Depending on the used data and report layout we can suggest you some custom approach using user-defined functions to set the action only if there is data or display alternative item without action.
In order to provide you more adequate suggestions, please share the report definition and data structure. Feel free to open a support ticket and send us there the requested details.
Have you tried the new visualization options in Telerik Reporting Q2 2013? You can get them from your account.