             guard nextIndex < lastIndex else { return nil }
             
             let nextKey = self.orderedKeys[nextIndex]
-            guard let nextValue = self.keysToValues[nextKey] else { fatalError("Inconsistency error occured in OrderedDictionary.") }
+            
+            guard let nextValue = self.keysToValues[nextKey] else {
+                fatalError("Inconsistency error occured in OrderedDictionary")
+            }
+            
             let element = (nextKey, nextValue)
             
             nextIndex++

    
    public mutating func removeValueForKey(key: Key) -> Value? {
        if let index = orderedKeys.indexOf(key) {
            orderedKeys.removeAtIndex(index)
            guard let currentValue = keysToValues[key] else { fatalError("Inconsistency error occured in OrderedDictionary.") }
            keysToValues[key] = nil
            return currentValue
        } else {
            return nil

    
    public mutating func updateValue(value: Value, forKey key: Key) -> Value? {
        if orderedKeys.contains(key) {
            guard let currentValue = keysToValues[key] else {
                fatalError("Inconsistency error occured in OrderedDictionary")
            }
            
            keysToValues[key] = value
            return currentValue
        } else {
