diff --git a/Ical.Net/DataTypes/CalDateTime.cs b/Ical.Net/DataTypes/CalDateTime.cs
index 10a891fd7..7fa81b469 100644
--- a/Ical.Net/DataTypes/CalDateTime.cs
+++ b/Ical.Net/DataTypes/CalDateTime.cs
@@ -228,7 +228,7 @@ private void CopyFrom(CalDateTime calDt)
         _tzId = calDt._tzId;
     }
 
-    public bool Equals(CalDateTime other) => this == other;
+    public bool Equals(CalDateTime? other) => this == other;
 
     /// <inheritdoc/>
     public override bool Equals(object? obj)
@@ -598,22 +598,22 @@ public CalDateTime AddDays(int days)
     /// <summary>
     /// Returns <see langword="true"/> if the current <see cref="CalDateTime"/> instance is less than <paramref name="dt"/>.
     /// </summary>
-    public bool LessThan(CalDateTime dt) => this < dt;
+    public bool LessThan(CalDateTime? dt) => this < dt;
 
     /// <summary>
     /// Returns <see langword="true"/> if the current <see cref="CalDateTime"/> instance is greater than <paramref name="dt"/>.
     /// </summary>
-    public bool GreaterThan(CalDateTime dt) => this > dt;
+    public bool GreaterThan(CalDateTime? dt) => this > dt;
 
     /// <summary>
     /// Returns <see langword="true"/> if the current <see cref="CalDateTime"/> instance is less than or equal to <paramref name="dt"/>.
     /// </summary>
-    public bool LessThanOrEqual(CalDateTime dt) => this <= dt;
+    public bool LessThanOrEqual(CalDateTime? dt) => this <= dt;
 
     /// <summary>
     /// Returns <see langword="true"/> if the current <see cref="CalDateTime"/> instance is greater than or equal to <paramref name="dt"/>.
     /// </summary>
-    public bool GreaterThanOrEqual(CalDateTime dt) => this >= dt;
+    public bool GreaterThanOrEqual(CalDateTime? dt) => this >= dt;
 
     /// <summary>
     /// Compares the current instance with another <see cref="CalDateTime"/> object and returns an integer that indicates whether the current instance precedes, follows, or occurs in the same position in the sort order as the other CalDateTime.
diff --git a/Ical.Net/Evaluation/EvaluationException.cs b/Ical.Net/Evaluation/EvaluationException.cs
index 5d592806a..78eaccdb8 100644
--- a/Ical.Net/Evaluation/EvaluationException.cs
+++ b/Ical.Net/Evaluation/EvaluationException.cs
@@ -3,6 +3,7 @@
 // Licensed under the MIT license.
 //
 
+#nullable enable
 using System;
 
 namespace Ical.Net.Evaluation;
diff --git a/Ical.Net/Evaluation/EvaluationLimitExceededException.cs b/Ical.Net/Evaluation/EvaluationLimitExceededException.cs
index f86fb1fb9..ceedf29dc 100644
--- a/Ical.Net/Evaluation/EvaluationLimitExceededException.cs
+++ b/Ical.Net/Evaluation/EvaluationLimitExceededException.cs
@@ -3,6 +3,7 @@
 // Licensed under the MIT license.
 //
 
+#nullable enable
 namespace Ical.Net.Evaluation;
 
 /// <summary>
diff --git a/Ical.Net/Evaluation/EvaluationOptions.cs b/Ical.Net/Evaluation/EvaluationOptions.cs
index da8bf5bb0..17e7ceb14 100644
--- a/Ical.Net/Evaluation/EvaluationOptions.cs
+++ b/Ical.Net/Evaluation/EvaluationOptions.cs
@@ -3,7 +3,9 @@
 // Licensed under the MIT license.
 //
 
+#nullable enable
 namespace Ical.Net.Evaluation;
+
 public class EvaluationOptions
 {
     /// <summary>
@@ -12,7 +14,7 @@ public class EvaluationOptions
     /// </summary>
     /// <remarks>
     /// This option only applies to the evaluation of RecurrencePatterns.
-    ///
+    /// <para/>
     /// If the specified number of increments is exceeded without finding a recurrence, an
     /// exception of type <see cref="Ical.Net.Evaluation.EvaluationLimitExceededException"/> will be thrown.
     /// </remarks>
diff --git a/Ical.Net/Evaluation/Evaluator.cs b/Ical.Net/Evaluation/Evaluator.cs
index 9569f3fab..c967bb96b 100644
--- a/Ical.Net/Evaluation/Evaluator.cs
+++ b/Ical.Net/Evaluation/Evaluator.cs
@@ -48,5 +48,5 @@ protected void IncrementDate(ref CalDateTime dt, RecurrencePattern pattern, int
         }
     }
 
-    public abstract IEnumerable<Period> Evaluate(CalDateTime referenceDate, CalDateTime? periodStart, CalDateTime? periodEnd, EvaluationOptions options);
+    public abstract IEnumerable<Period> Evaluate(CalDateTime referenceDate, CalDateTime? periodStart, CalDateTime? periodEnd, EvaluationOptions? options);
 }
diff --git a/Ical.Net/Evaluation/IEvaluator.cs b/Ical.Net/Evaluation/IEvaluator.cs
index 8232aa70a..92a8e27e1 100644
--- a/Ical.Net/Evaluation/IEvaluator.cs
+++ b/Ical.Net/Evaluation/IEvaluator.cs
@@ -37,5 +37,5 @@ public interface IEvaluator
     ///     A sequence of <see cref="Ical.Net.DataTypes.Period"/> objects for
     ///     each date/time when this item occurs/recurs.
     /// </returns>
-    IEnumerable<Period> Evaluate(CalDateTime referenceDate, CalDateTime? periodStart, CalDateTime? periodEnd, EvaluationOptions options);
+    IEnumerable<Period> Evaluate(CalDateTime referenceDate, CalDateTime? periodStart, CalDateTime? periodEnd, EvaluationOptions? options);
 }
diff --git a/Ical.Net/Evaluation/RecurrenceUtil.cs b/Ical.Net/Evaluation/RecurrenceUtil.cs
index 594a8ed4d..78dbf154c 100644
--- a/Ical.Net/Evaluation/RecurrenceUtil.cs
+++ b/Ical.Net/Evaluation/RecurrenceUtil.cs
@@ -3,21 +3,20 @@
 // Licensed under the MIT license.
 //
 
-using System;
+#nullable enable
 using System.Collections.Generic;
 using System.Linq;
 using Ical.Net.CalendarComponents;
 using Ical.Net.DataTypes;
-using Ical.Net.Utility;
 
 namespace Ical.Net.Evaluation;
 
 internal class RecurrenceUtil
 {
-    public static IEnumerable<Occurrence> GetOccurrences(IRecurrable recurrable, CalDateTime dt, EvaluationOptions options = default) => GetOccurrences(recurrable,
+    public static IEnumerable<Occurrence> GetOccurrences(IRecurrable recurrable, CalDateTime dt, EvaluationOptions? options = null) => GetOccurrences(recurrable,
         new CalDateTime(dt.Date), new CalDateTime(dt.Date.AddDays(1)), options);
 
-    public static IEnumerable<Occurrence> GetOccurrences(IRecurrable recurrable, CalDateTime periodStart, CalDateTime periodEnd, EvaluationOptions options = default)
+    public static IEnumerable<Occurrence> GetOccurrences(IRecurrable recurrable, CalDateTime? periodStart, CalDateTime? periodEnd, EvaluationOptions? options = null)
     {
         var evaluator = recurrable.Evaluator;
         if (evaluator == null || recurrable.Start == null)
@@ -43,7 +42,9 @@ from p in periods
             let endTime = p.EndTime ?? p.StartTime
             where
                 (((periodStart == null) || endTime.GreaterThan(periodStart)) && ((periodEnd == null) || p.StartTime.LessThan(periodEnd)) ||
-                (periodStart.Equals(periodEnd) && p.StartTime.LessThanOrEqual(periodStart) && endTime.GreaterThan(periodEnd))) || //A period that starts at the same time it ends
+                (periodStart != null && periodStart.Equals(periodEnd)
+                 && p.StartTime.LessThanOrEqual(periodStart)
+                 && endTime.GreaterThan(periodEnd))) || //A period that starts at the same time it ends
                 (p.StartTime.Equals(endTime) && p.StartTime.Equals(periodStart)) //An event that starts at the same time it ends
             select new Occurrence(recurrable, p);
 
@@ -56,16 +57,16 @@ from p in periods
         switch (p.Frequency)
         {
             case FrequencyType.Minutely:
-                return new bool?[] { false, null, false, false, false, false, false, true, false };
+                return [false, null, false, false, false, false, false, true, false];
             case FrequencyType.Hourly:
-                return new bool?[] { false, null, false, false, false, false, true, true, false };
+                return [false, null, false, false, false, false, true, true, false];
             case FrequencyType.Daily:
-                return new bool?[] { false, null, null, false, false, true, true, true, false };
+                return [false, null, null, false, false, true, true, true, false];
             case FrequencyType.Weekly:
-                return new bool?[] { false, null, null, null, true, true, true, true, false };
+                return [false, null, null, null, true, true, true, true, false];
             case FrequencyType.Monthly:
                 {
-                    var row = new bool?[] { false, null, null, true, true, true, true, true, false };
+                    bool?[] row = [false, null, null, true, true, true, true, true, false];
 
                     // Limit if BYMONTHDAY is present; otherwise, special expand for MONTHLY.
                     if (p.ByMonthDay.Count > 0)
@@ -77,7 +78,7 @@ from p in periods
                 }
             case FrequencyType.Yearly:
                 {
-                    var row = new bool?[] { true, true, true, true, true, true, true, true, false };
+                    bool?[] row = [true, true, true, true, true, true, true, true, false];
 
                     // Limit if BYYEARDAY or BYMONTHDAY is present; otherwise,
                     // special expand for WEEKLY if BYWEEKNO present; otherwise,
@@ -91,7 +92,7 @@ from p in periods
                     return row;
                 }
             default:
-                return new bool?[] { false, null, false, false, false, false, false, false, false };
+                return [false, null, false, false, false, false, false, false, false];
         }
     }
 }
diff --git a/Ical.Net/Evaluation/RecurringEvaluator.cs b/Ical.Net/Evaluation/RecurringEvaluator.cs
index 4f576a12f..d1aa9549a 100644
--- a/Ical.Net/Evaluation/RecurringEvaluator.cs
+++ b/Ical.Net/Evaluation/RecurringEvaluator.cs
@@ -4,7 +4,6 @@
 //
 
 #nullable enable
-using System;
 using System.Collections.Generic;
 using System.Linq;
 using Ical.Net.CalendarComponents;