xcode - iOS error with UIAlertController (CGContextAddPath, CGContextAddPath) brings strange behavior in my app -

in ios application errors when try use uialertcontroller show alert information user , after error appears progress bar not updating progress line.

my code looks this:

// create alert let alert = uialertcontroller(title: "my title", message: "this message.", preferredstyle: uialertcontrollerstyle.alert)  // add action (button) alert.addaction(uialertaction(title: "ok", style: uialertactionstyle.default, handler: nil))  // show alert self.presentviewcontroller(alert, animated: true, completion: nil) 

this code runs inside uiviewcontroller under xcode version 7.3 (7d175) on iphone 6 simulator.

and i'm getting type of errors:

apr  6 14:36:29  timerapp[32952] <error>: cgcontextaddpath: invalid context 0x0. if want see backtrace, please set cg_context_show_backtrace environmental variable. apr  6 14:36:29  timerapp[32952] <error>: clip: invalid context 0x0. if want see backtrace, please set cg_context_show_backtrace environmental variable. apr  6 14:36:29  timerapp[32952] <error>: cgcontextdrawlineargradient: invalid context 0x0. if want see backtrace, please set cg_context_show_backtrace environmental variable. apr  6 14:36:31  timerapp[32952] <error>: cgcontextaddpath: invalid context 0x0. if want see backtrace, please set cg_context_show_backtrace environmental variable. apr  6 14:36:31  timerapp[32952] <error>: clip: invalid context 0x0. if want see backtrace, please set cg_context_show_backtrace environmental variable. apr  6 14:36:31  timerapp[32952] <error>: cgcontextdrawlineargradient: invalid context 0x0. if want see backtrace, please set cg_context_show_backtrace environmental variable. 

i tried google bug , found posts update xcode xcode latest version. can avoid errors?