Make RucrrencePattern.Count nullable to avoid using magic number `i…

…nt.MinValue`.

Ical.Net/DataTypes/RecurrencePattern.cs

@@ -29,7 +29,7 @@ public class RecurrencePattern : EncodableDataType
 
     public DateTime? Until { get; set; }
 
-    public int Count { get; set; } = int.MinValue;
+    public int? Count { get; set; }
 
     /// <summary>
     /// Specifies how often the recurrence should repeat.
@@ -181,7 +181,7 @@ public override int GetHashCode()
 #pragma warning restore 0618
             hashCode = (hashCode * 397) ^ (int) Frequency;
             hashCode = (hashCode * 397) ^ Until.GetHashCode();
-            hashCode = (hashCode * 397) ^ Count;
+            hashCode = (hashCode * 397) ^ (Count ?? 0);
             hashCode = (hashCode * 397) ^ (int) FirstDayOfWeek;
             hashCode = (hashCode * 397) ^ CollectionHelpers.GetHashCode(BySecond);
             hashCode = (hashCode * 397) ^ CollectionHelpers.GetHashCode(ByMinute);

Ical.Net/Evaluation/RecurrencePatternEvaluator.cs

@@ -221,14 +221,18 @@ private IEnumerable<DateTime> GetDates(IDateTime seed, DateTime? periodStart, Da
 
         // optimize the start time for selecting candidates
         // (only applicable where a COUNT is not specified)
-        if (pattern.Count == int.MinValue)
+        if (pattern.Count is null)
         {
             var incremented = seedCopy;
             while (incremented < periodStart)
             {
                 seedCopy = incremented;
                 IncrementDate(ref incremented, pattern, pattern.Interval);
             }
+        } else
+        {
+            if (pattern.Count < 1)
+                throw new Exception("Count must be greater than 0");
         }
 
         // Do the enumeration in a separate method, as it is a generator method that is
@@ -256,7 +260,7 @@ private IEnumerable<DateTime> EnumerateDates(DateTime originalDate, DateTime see
                 break;
             }
 
-            if (pattern.Count >= 1 && dateCount >= pattern.Count)
+            if (dateCount >= pattern.Count)
             {
                 break;
             }
@@ -281,7 +285,7 @@ private IEnumerable<DateTime> EnumerateDates(DateTime originalDate, DateTime see
                     // from the previous year.
                     //
                     // exclude candidates that start at the same moment as periodEnd if the period is a range but keep them if targeting a specific moment
-                    if (pattern.Count >= 1 && dateCount >= pattern.Count)
+                    if (dateCount >= pattern.Count)
                     {
                         break;
                     }

Ical.Net/Evaluation/TodoEvaluator.cs

@@ -65,7 +65,7 @@ private void DetermineStartingRecurrence(PeriodList rdate, ref IDateTime referen
 
     private void DetermineStartingRecurrence(RecurrencePattern recur, ref IDateTime referenceDateTime)
     {
-        if (recur.Count != int.MinValue)
+        if (recur.Count.HasValue)
         {
             referenceDateTime = Todo.Start.Copy<IDateTime>();
         }

Ical.Net/Serialization/DataTypes/RecurrencePatternSerializer.cs

@@ -58,12 +58,27 @@ public virtual void CheckRange(string name, IList<int> values, int min, int max)
         }
     }
 
+    public virtual void CheckRange(string name, IList<int?> values, int min, int max)
+    {
+        var allowZero = (min == 0 || max == 0);
+        foreach (var value in values)
+        {
+            CheckRange(name, value, min, max, allowZero);
+        }
+    }
+
     public virtual void CheckRange(string name, int value, int min, int max)
     {
         var allowZero = min == 0 || max == 0;
         CheckRange(name, value, min, max, allowZero);
     }
 
+    public virtual void CheckRange(string name, int? value, int min, int max)
+    {
+        var allowZero = min == 0 || max == 0;
+        CheckRange(name, value, min, max, allowZero);
+    }
+
     public virtual void CheckRange(string name, int value, int min, int max, bool allowZero)
     {
         if (value != int.MinValue && (value < min || value > max || (!allowZero && value == 0)))
@@ -73,6 +88,15 @@ public virtual void CheckRange(string name, int value, int min, int max, bool al
         }
     }
 
+    public virtual void CheckRange(string name, int? value, int min, int max, bool allowZero)
+    {
+        if (value != null && (value < min || value > max || (!allowZero && value == 0)))
+        {
+            throw new ArgumentException(name + " value " + value + " is out of range. Valid values are between " + min + " and " + max +
+                                        (allowZero ? "" : ", excluding zero (0)") + ".");
+        }
+    }
+
     public virtual void CheckMutuallyExclusive<T, TU>(string name1, string name2, T obj1, TU obj2)
     {
         if (Equals(obj1, default(T)) || Equals(obj2, default(TU)))
@@ -160,7 +184,7 @@ public override string SerializeToString(object obj)
             values.Add("WKST=" + Enum.GetName(typeof(DayOfWeek), recur.FirstDayOfWeek).ToUpper().Substring(0, 2));
         }
 
-        if (recur.Count != int.MinValue)
+        if (recur.Count.HasValue)
         {
             values.Add("COUNT=" + recur.Count);
         }