title: Terminating app due to uncaught exception 'NSGenericException', reason: '*** Collection <__NSSetM...> was mutated while being enumerated.'
body: <p>I don't understand problem, but I guess the problem in storyboard (In my constraints, because sometimes objects isn't where they must be). </p>
  
  <p><strong>* Terminating app due to uncaught exception 'NSGenericException', reason: '*</strong> </p>
  
  <pre><code>Collection &lt;__NSSetM: 0x7fae0b5e6900&gt; was mutated while being enumerated.'
  *** First throw call stack:
  
   - (
      0   CoreFoundation   __exceptionPreprocess + 165
  
      1   libobjc.A.dylib  objc_exception_throw + 45
  
      2   CoreFoundation __NSFastEnumerationMutationHandler + 132
  
      3   Foundation  -[NSISEngine substituteOutAllOccurencesOfBodyVar:withExpression:] + 336
  
      4   Foundation -[NSISEngine pivotToMakeBodyVar:newHeadOfRowWithHead:andDropRow:] + 330
  
      5   Foundation   -[NSISEngine minimizeConstantInObjectiveRowWithHead:] + 314
  
      6   Foundation  -[NSISEngine tryUsingArtificialVariableToAddConstraintWithMarker:rowBody:usingInfeasibilityHandlingBehavior:mutuallyExclusiveConstraints:] + 285
  
      7   Foundation  -[NSISEngine tryToAddConstraintWithMarker:expression:integralizationAdjustment:mutuallyExclusiveConstraints:] + 691
  
      8   Foundation   -[NSLayoutConstraint _addLoweredExpression:toEngine:integralizationAdjustment:lastLoweredConstantWasRounded:mutuallyExclusiveConstraints:] + 275
  
      9   Foundation   -[NSLayoutConstraint _addToEngine:integralizationAdjustment:mutuallyExclusiveConstraints:] + 220
  
      10  UIKit  -[UIView(UIConstraintBasedLayout) _layoutEngine_didAddLayoutConstraint:roundingAdjustment:mutuallyExclusiveConstraints:] + 411
  
      11  UIKit -[UIView(UIConstraintBasedLayout) _tryToAddConstraintWithoutUpdatingConstraintsArray:roundingAdjustment:mutuallyExclusiveConstraints:] + 30
  
      12  UIKit [UIView(UIConstraintBasedLayout) _tryToAddConstraint:roundingAdjustment:mutuallyExclusiveConstraints:] + 243
  
      13  UIKit -[UIView(UIConstraintBasedLayout) addConstraints:]_block_invoke + 188
  
      14  Foundation [NSISEngine withBehaviors:performModifications:] + 155
  
      15  UIKit  [UIView(UIConstraintBasedLayout) addConstraints:] + 263
  
      16  UIKit-[UIView _setTraitStorageConstraints:] + 794
  </code></pre>