diff --git a/TwitchDownloaderCore.Tests/ToolTests/FilenameServiceTests.cs b/TwitchDownloaderCore.Tests/ToolTests/FilenameServiceTests.cs
index 078607d8..2a6a02cc 100644
--- a/TwitchDownloaderCore.Tests/ToolTests/FilenameServiceTests.cs
+++ b/TwitchDownloaderCore.Tests/ToolTests/FilenameServiceTests.cs
@@ -1,5 +1,4 @@
-using TwitchDownloaderCore.Extensions;
-using TwitchDownloaderCore.Tools;
+using TwitchDownloaderCore.Tools;
 
 namespace TwitchDownloaderCore.Tests.ToolTests
 {
@@ -148,6 +147,17 @@ public void DoesNotInterpretBogusTemplateParameter()
             Assert.Equal(EXPECTED, result);
         }
 
+        [Fact]
+        public void GetFilenameDoesNotThrow_WhenNullOrDefaultInput()
+        {
+            const string TEMPLATE = "{title}_{id}_{date}_{channel}_{trim_start}_{trim_end}_{length}_{views}_{game}_{date_custom=\"s\"}_{trim_start_custom=\"hh\\-mm\\-ss\"}_{trim_end_custom=\"hh\\-mm\\-ss\"}_{length_custom=\"hh\\-mm\\-ss\"}";
+            const string EXPECTED = "__1-1-01__00-00-00_00-00-00_00-00-00_0__0001-01-01T00_00_00_00-00-00_00-00-00_00-00-00";
+
+            var result = FilenameService.GetFilename(TEMPLATE, default, default, default, default, default, default, default, default);
+
+            Assert.Equal(EXPECTED, result);
+        }
+
         [Theory]
         [InlineData("\"", "＂")]
         [InlineData("*", "＊")]
@@ -166,6 +176,17 @@ public void CorrectlyReplacesInvalidFilenameCharacters(string str, string expect
             Assert.Equal(expected, actual);
         }
 
+        [Fact]
+        public void ReplaceInvalidFilenameCharactersDoesNotThrow_WhenNullInput()
+        {
+            const string? STR = null;
+            const string? EXPECTED = null;
+
+            var actual = FilenameService.ReplaceInvalidFilenameChars(STR);
+
+            Assert.Equal(EXPECTED, actual);
+        }
+
         [Fact]
         public void GetNonCollidingNameWorks_WhenNoCollisionExists()
         {
diff --git a/TwitchDownloaderCore/Tools/FilenameService.cs b/TwitchDownloaderCore/Tools/FilenameService.cs
index 8f73faeb..8ae0ddf2 100644
--- a/TwitchDownloaderCore/Tools/FilenameService.cs
+++ b/TwitchDownloaderCore/Tools/FilenameService.cs
@@ -1,4 +1,5 @@
 using System;
+using System.Diagnostics.CodeAnalysis;
 using System.Globalization;
 using System.IO;
 using System.Text;
@@ -9,7 +10,7 @@ namespace TwitchDownloaderCore.Tools
 {
     public static class FilenameService
     {
-        public static string GetFilename(string template, string title, string id, DateTime date, string channel, TimeSpan trimStart, TimeSpan trimEnd, long viewCount, string game)
+        public static string GetFilename(string template, [AllowNull] string title, [AllowNull] string id, DateTime date, [AllowNull] string channel, TimeSpan trimStart, TimeSpan trimEnd, long viewCount, [AllowNull] string game)
         {
             var videoLength = trimEnd - trimStart;
 
@@ -86,8 +87,14 @@ private static string[] GetTemplateSubfolders(ref string fullPath)
 
         private static readonly char[] FilenameInvalidChars = Path.GetInvalidFileNameChars();
 
-        public static string ReplaceInvalidFilenameChars(string filename)
+        [return: NotNullIfNotNull(nameof(filename))]
+        public static string ReplaceInvalidFilenameChars([AllowNull] string filename)
         {
+            if (string.IsNullOrEmpty(filename))
+            {
+                return filename;
+            }
+
             const string TIMESTAMP_PATTERN = /*lang=regex*/ @"(?<=\d):(?=\d\d)";
             var newName = Regex.Replace(filename, TIMESTAMP_PATTERN, "_");