I've built a custom NSURLProtocol which is used by a WebView whilst it browses. But at seemingly random times (between a 20 seconds or a few minutes into browsing) I am getting an EXC_BREAKPOINT and the app stops running in my NSURLProtocol.
The relevant part of my NSURLProtocol is below, it's the last line which is showing the EXC_BREAKPOINT
self.mutableData = NSMutableData(data: data!)
self.response = response
self.client?.URLProtocol(self, didReceiveResponse: response!, cacheStoragePolicy: NSURLCacheStoragePolicy.Allowed)
self.client?.URLProtocol(self, didLoadData: data!)
self.client?.URLProtocolDidFinishLoading(self)The Xcode error is visible below: 
I'm totally bamboozled on this one. Does anyone have an idea what might be causing this, and how to fix it?
Thank you!
Sam