set-transportservice back to its default value.

Hi Everyone, 

Here is a quick question that I want to ask?

During configuration of the Exchange Server 2013, as I was troubleshooting the exchange server's mail flow, I have used the following cmdlet to change the Transportservice InternalDNSServers

set-transportservice -InternalDNSServers 192.168.x.x 

Now, i know that the default value for this is null, and would like to revert to back to it. How does one do it as it won't accept $false or {null}. Any help would be greatly appreciated. 

Thank you so much! 

PS The IP address i pointed to is our local DNS server.