GUACAMOLE-197: You can't throw something after you return out of the function, so lets remove the return statement.

extensions/guacamole-auth-radius/src/main/java/org/apache/guacamole/auth/radius/AuthenticationProviderService.java

@@ -131,7 +131,6 @@ public class AuthenticationProviderService {
             catch(UnknownAttributeException e) {
                 logger.error("Error in talks with RADIUS server.");
                 logger.debug("RADIUS challenged by didn't provide right attributes.");
-                return null;
                 throw new GuacamoleInvalidCredentialsException("Authentication error.", CredentialsInfo.USERNAME_PASSWORD);
             }
         }