After reading the documentation I found that there are some error codes for various situations. For example there is an error 15 if there is no result found.
I want to use XML service for my application but after testing the service I see that there is no error code provided as the documentation talks about.
For the findNearestAddress it is not considered an exception to not find an address. I would even estimate that it is normal for this service to not find an address, the US is not so densely populated that each coordinate is close to an address.