refactor: remove redundant null checks

SongTidy.Tests/FilenameParserTests.cs

@@ -231,18 +231,6 @@ public sealed class FilenameParserTests {
 
     #endregion
 
-    #region Argument validation
-
-    /// <summary>
-    /// Verifies that a null input is rejected.
-    /// </summary>
-    [TestMethod]
-    public void ThrowsForNullInput() {
-        Assert.Throws<ArgumentNullException>(() => FilenameParser.Parse(null!));
-    }
-
-    #endregion
-
     /// <summary>
     /// Parses the input and asserts all three resulting fields.
     /// </summary>

SongTidy.Tests/RenameFormatsTests.cs

@@ -114,15 +114,6 @@ public sealed class RenameFormatsTests {
         AssertStem(RenameFormat.ArtistFirst, "   ", "Title", "\t", "Title");
     }
 
-    /// <summary>
-    /// Verifies that a null title is rejected.
-    /// </summary>
-    [TestMethod]
-    public void ThrowsForNullTitle() {
-        Assert.Throws<ArgumentNullException>(
-            () => RenameFormats.GenerateStem(RenameFormat.ArtistFirst, "Artist", null!, "Live"));
-    }
-
     #endregion
 
     /// <summary>

SongTidy/Models/RenameFormats.cs

@@ -109,10 +109,6 @@ public static class RenameFormats {
     /// Whitespace-only optional fields are treated as missing.
     /// </remarks>
     public static string GenerateStem(RenameFormat format, string artist, string title, string comment) {
-        ArgumentNullException.ThrowIfNull(artist);
-        ArgumentNullException.ThrowIfNull(title);
-        ArgumentNullException.ThrowIfNull(comment);
-
         RenameFormatDefinition definition = GetDefinition(format);
         bool hasArtist = !string.IsNullOrWhiteSpace(artist);
         bool hasComment = !string.IsNullOrWhiteSpace(comment);

SongTidy/Services/FilenameParser.cs

@@ -1,4 +1,3 @@
-using System;
 using System.Collections.Generic;
 using System.Text;
 
@@ -22,8 +21,6 @@ public static class FilenameParser {
     /// When no hyphen or more than one hyphen remains, the artist is empty and the whole text is the title.
     /// </remarks>
     public static FilenameParseResult Parse(string fileNameWithoutExtension) {
-        ArgumentNullException.ThrowIfNull(fileNameWithoutExtension);
-
         string source = fileNameWithoutExtension;
         string comment = string.Empty;