Use the system's TimeZoneInfo.Utc cache.

This should be safer if someone calls ClearCachedData.

Author: airbreather

src/NetTopologySuite.IO.GPX/GpxReaderSettings.cs

@@ -8,16 +8,25 @@ namespace NetTopologySuite.IO
     /// </summary>
     public sealed class GpxReaderSettings
     {
-        private static readonly TimeZoneInfo UtcTimeZone = TimeZoneInfo.Utc;
-
         private static readonly GpxExtensionReader DefaultExtensionReader = new GpxExtensionReader();
 
+        private TimeZoneInfo timeZoneInfo;
+
         /// <summary>
         /// Gets or sets the <see cref="System.TimeZoneInfo"/> instance that the system should use
         /// to interpret timestamps in the GPX file, when the file itself does not contain time zone
         /// information.  Default is <see cref="TimeZoneInfo.Utc"/>.
+        /// <para>
+        /// <see langword="null"/> is treated as <see cref="TimeZoneInfo.Utc"/>, but please prefer
+        /// <see langword="null"/> so that <see cref="TimeZoneInfo.ClearCachedData"/> does not
+        /// affect our correctness.
+        /// </para>
         /// </summary>
-        public TimeZoneInfo TimeZoneInfo { get; set; } = UtcTimeZone;
+        public TimeZoneInfo TimeZoneInfo
+        {
+            get => this.timeZoneInfo ?? TimeZoneInfo.Utc;
+            set => this.timeZoneInfo = value;
+        }
 
         /// <summary>
         /// Gets or sets the <see cref="GpxExtensionReader"/> instance to use to convert GPX

src/NetTopologySuite.IO.GPX/GpxWriterSettings.cs

@@ -8,17 +8,26 @@ namespace NetTopologySuite.IO
     /// </summary>
     public sealed class GpxWriterSettings
     {
-        private static readonly TimeZoneInfo UtcTimeZone = TimeZoneInfo.Utc;
-
         private static readonly GpxExtensionWriter DefaultExtensionWriter = new GpxExtensionWriter();
 
+        private TimeZoneInfo timeZoneInfo;
+
         /// <summary>
         /// Gets or sets the <see cref="System.TimeZoneInfo"/> instance that the system should use
         /// to produce timestamps for the GPX file.  Default is <see cref="TimeZoneInfo.Utc"/>.
         /// When overwriting this property, note that the XSD schema specifies that, by convention,
         /// timestamps in GPX files are expected to be in UTC.
+        /// <para>
+        /// <see langword="null"/> is treated as <see cref="TimeZoneInfo.Utc"/>, but please prefer
+        /// <see langword="null"/> so that <see cref="TimeZoneInfo.ClearCachedData"/> does not
+        /// affect our correctness.
+        /// </para>
         /// </summary>
-        public TimeZoneInfo TimeZoneInfo { get; set; } = UtcTimeZone;
+        public TimeZoneInfo TimeZoneInfo
+        {
+            get => this.timeZoneInfo ?? TimeZoneInfo.Utc;
+            set => this.timeZoneInfo = value;
+        }
 
         /// <summary>
         /// Gets or sets the <see cref="GpxExtensionWriter"/> instance to use to convert