title: mutating method sent to immutable object - error
body: <pre><code>NSUserDefaults *defaultDefects = [NSUserDefaults standardUserDefaults];
      NSLog(@"%f %f", self.defectPositionX, self.defectPositionY);
  
  NSMutableArray *loadDefects = [defaultDefects objectForKey:@"defaultDefects"];
      NSLog(@"%f %f", self.defectPositionX, self.defectPositionY);
  if (loadDefects == nil) {
      loadDefects = [NSMutableArray array];
  }
      NSLog(@"%f %f", self.defectPositionX, self.defectPositionY);
  //PROBLEM HERE
  [loadDefects addObject:[NSNumber numberWithDouble:self.defectPositionX ]];
  [loadDefects addObject:[NSNumber numberWithDouble:self.defectPositionY ]];
  NSLog(@"%f %f", self.defectPositionX, self.defectPositionY);
  
  
  [defaultDefects setObject:loadDefects forKey:@"defaultDefects"];
  NSLog(@"%f %f", self.defectPositionX, self.defectPositionY);
  
  [defaultDefects synchronize];
  NSLog(@"%f %f", self.defectPositionX, self.defectPositionY);
  
  
  ViewControllerImage *secondViewController = [self.storyboard instantiateViewControllerWithIdentifier:@"ViewControllerImage"];
  secondViewController.thicknessValue1 = self.thicknessValue1;
  secondViewController.capWidthValue1 = self.capWidthValue1;
  NSLog(@"%f %f", self.defectPositionX, self.defectPositionY);
  
  [self presentViewController:secondViewController animated:YES completion:nil];
  NSLog(@"%f %f", self.defectPositionX, self.defectPositionY);
  </code></pre>
  
  <p>Logs this</p>
  
  <pre><code>2014-04-21 17:03:02.838 U[8958:60b] 169.728546 274.674475
  2014-04-21 17:03:02.840 U[8958:60b] 169.728546 274.674475
  2014-04-21 17:03:02.842 U[8958:60b] 169.728546 274.674475
  </code></pre>
  
  <p>The full error report is this</p>
  
  <p><strong>* Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: '-[__NSCFArray insertObject:atIndex:]: mutating method sent to immutable object'
  *</strong> First throw call stack:
  (0x2e8e2f03 0x39077ce7 0x2e8e2e45 0x2e85642b 0xb93d3 0x311476c7 0x31147663 0x31147633 0x31132d7b 0x3114fa3d 0x31146c7d 0x31141ca7 0x31116e75 0x31115541 0x2e8adfe7 0x2e8ad4af 0x2e8abc9f 0x2e8167a9 0x2e81658b 0x337836d3 0x31175891 0xb7851 0x39575ab7)
  libc++abi.dylib: terminating with uncaught exception of type NSException</p>
  
  <p>I am confused at how I have it as a Mutable Array yet it's calling it Immutable meaning I cannot mutate it.. It's the first time I've come across this error and I am struggling to grasp it.</p>
  
  <p>When running the app and I save the data into the mutable array, sometimes it works and then sometimes it crashes...?</p>