Fixed bug finding occurrence with 0 ticks.

src/Cronos/CronExpression.cs

@@ -34,7 +34,7 @@ namespace Cronos
     /// </summary>
     public sealed class CronExpression: IEquatable<CronExpression>
     {
-        private const long NotFound = 0;
+        private const long NotFound = -1;
         private const int MaxYear = 2499;
 
         /// <summary>

tests/Cronos.Tests/CronExpressionFacts.cs

@@ -2456,6 +2456,18 @@ public void GetNextOccurrence_ReturnsCorrectDate_When6fieldsExpressionIsUsedAndI
             Assert.Equal(GetInstantFromLocalTime(expectedString, EasternTimeZone), nextOccurrence);
         }
 
+        [Fact]
+        public void GetNextOccurrence_FromDateTimeMinValueInclusive_SuccessfullyReturned()
+        {
+            var expression = CronExpression.Parse("* * * * *");
+            var from = new DateTime(0, DateTimeKind.Utc);
+
+            var occurrence = expression
+                .GetNextOccurrence(from, inclusive: true);
+
+            Assert.Equal(from, occurrence);
+        }
+
         [Fact]
         public void GetOccurrence_PassesTests_DefinedInTheGitHubIssue53()
         {
@@ -2741,6 +2753,20 @@ public void GetOccurrences_DateTimeOffset_HandlesToInclusiveArgument()
             Assert.Equal(from.AddMinutes(2), occurrences[2].UtcDateTime);
         }
 
+        [Fact]
+        public void GetOccurrences_OccurrenceAtDateTimeMinValue_SuccessfullyReturned()
+        {
+            var expression = CronExpression.Parse("* * * * *");
+            var from = new DateTime(0, DateTimeKind.Utc);
+
+            var occurrences = expression
+                .GetOccurrences(from, from.AddSeconds(1), fromInclusive: true)
+                .ToArray();
+
+            Assert.Single(occurrences);
+            Assert.Equal(from, occurrences[0]);
+        }
+
         [Theory]
         [InlineData("* * * * *", "* * * * *")]