-initWithBaseURL: will now raise an exception with a nil URL parameter. This enforces what the code comments say.

Without this, Reachability might cause the application to crash on iOS 6 if the baseURL is nil.

AFNetworking/AFHTTPClient.m

@@ -238,6 +238,10 @@ static NSString * AFPropertyListStringFromParameters(NSDictionary *parameters) {
         return nil;
     }
 	
+	if (!url) {
+		[NSException raise:@"-[AFHTTPClient initWithBaseURL:] nil URL" format:@"`url` must not be nil"];
+	}
+    
     // Ensure terminal slash for baseURL path, so that NSURL +URLWithString:relativeToURL: works as expected
     if ([[url path] length] > 0 && ![[url absoluteString] hasSuffix:@"/"]) {
         url = [url URLByAppendingPathComponent:@""];