Terminating app due to uncaught exception error - uitextfield

Question

The app is supposed to save data in Text Fields when I click return on the keyboard. The app crashes when I click the return key. I have connected the IBActions to the textfields with "Did End on Exit" in .xib". Here is the error log:
Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[NSPlaceholderString initWithFormat:locale:arguments:]: nil argument'
*** First throw call stack:
(
0 CoreFoundation 0x0173b5e4 __exceptionPreprocess + 180
1 libobjc.A.dylib 0x014be8b6 objc_exception_throw + 44
2 CoreFoundation 0x0173b3bb +[NSException raise:format:] + 139
3 Foundation 0x010da664 -[NSPlaceholderString initWithFormat:locale:arguments:] + 99
4 Foundation 0x010da5f4 -[NSString initWithFormat:] + 58
5 Attendance 0x00002ded -[ShiftAController1 saveRoster1:] + 157
6 libobjc.A.dylib 0x014d081f -[NSObject performSelector:withObject:] + 70
7 UIKit 0x0022e0c2 -[UIApplication sendAction:to:from:forEvent:] + 108
8 UIKit 0x0022e04e -[UIApplication sendAction:toTarget:fromSender:forEvent:] + 61
9 UIKit 0x003260c1 -[UIControl sendAction:to:forEvent:] + 66
10 UIKit 0x00326484 -[UIControl _sendActionsForEvents:withEvent:] + 577
11 UIKit 0x0032da28 -[UIFieldEditor insertText:] + 263
12 UIKit 0x0091771f -[UITextField insertText:] + 59
13 UIKit 0x00409b40 -[UIKeyboardImpl insertText:] + 87
14 UIKit 0x0041af14 -[TIKeyboardOperationInsertText(UIKeyboardImpl) main] + 83
15 Foundation 0x01193829 -[__NSOperationInternal _start:] + 671
16 Foundation 0x01110558 -[NSOperation start] + 83
17 UIKit 0x004081cd -[UIKeyboardImpl performOperations:] + 153
18 UIKit 0x0040640b -[UIKeyboardImpl continueHandleKeyboardInputWithOperations:] + 40
19 UIKit 0x0040627c __73-[UIKeyboardImpl replyHandlerForHandleKeyboardInputWithExecutionContext:]_block_invoke_2 + 44
20 UIKit 0x0093b3c8 -[UIKeyboardTaskQueue continueExecutionOnMainThread] + 402
21 libobjc.A.dylib 0x014d081f -[NSObject performSelector:withObject:] + 70
22 Foundation 0x011139d8 __NSThreadPerformPerform + 285
23 CoreFoundation 0x016c483f __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 15
24 CoreFoundation 0x016c41cb __CFRunLoopDoSources0 + 235
25 CoreFoundation 0x016e129e __CFRunLoopRun + 910
26 CoreFoundation 0x016e0ac3 CFRunLoopRunSpecific + 467
27 CoreFoundation 0x016e08db CFRunLoopRunInMode + 123
28 GraphicsServices 0x036e09e2 GSEventRunModal + 192
29 GraphicsServices 0x036e0809 GSEventRun + 104
30 UIKit 0x0022cd3b UIApplicationMain + 1225
31 Attendance 0x00003a1d main + 141
32 libdyld.dylib 0x01d7970d start + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException
(lldb)
This is my code in .m:
-(IBAction)saveRoster1:(id)sender{
myString1 = [[NSString alloc] initWithFormat:roster1.text];
[roster1 setText:myString1];
NSUserDefaults *stringDefault1 = [NSUserDefaults standardUserDefaults];
[stringDefault1 setObject:myString1 forKey:#"stringKey1"];}
-(IBAction)savetimeIn:(id)sender{
myString2 = [[NSString alloc] initWithFormat:timeIn.text];
[timeIn setText:myString2];
NSUserDefaults *stringDefault2 = [NSUserDefaults standardUserDefaults];
[stringDefault2 setObject:myString2 forKey:#"stringKey2"];}
-(IBAction)savetimeOut:(id)sender{
myString3 = [[NSString alloc] initWithFormat:timeOut.text];
[timeOut setText:myString3];
NSUserDefaults *stringDefault3 = [NSUserDefaults standardUserDefaults];
[stringDefault3 setObject:myString3 forKey:#"stringKey3"];}