diff --git a/LrcParser.Tests/Parser/Lrc/Utils/LrcTimedTextUtilsTest.cs b/LrcParser.Tests/Parser/Lrc/Utils/LrcTimedTextUtilsTest.cs
index 6111bc3..8b26b74 100644
--- a/LrcParser.Tests/Parser/Lrc/Utils/LrcTimedTextUtilsTest.cs
+++ b/LrcParser.Tests/Parser/Lrc/Utils/LrcTimedTextUtilsTest.cs
@@ -15,7 +15,7 @@ public class LrcTimedTextUtilsTest
     [TestCase("[00:17:97]帰[00:18:37]り[00:18:55]道[00:18:94]は[00:19:22] ", "帰り道は ", new[] { "[0,start]:17970", "[1,start]:18370", "[2,start]:18550", "[3,start]:18940", "[3,end]:19220" })]
     [TestCase("帰[00:18:37]り[00:18:55]道[00:18:94]は[00:19:22]", "帰り道は", new[] { "[1,start]:18370", "[2,start]:18550", "[3,start]:18940", "[3,end]:19220" })]
     [TestCase("[00:17:97]帰[00:18:37]り[00:18:55]道[00:18:94]は", "帰り道は", new[] { "[0,start]:17970", "[1,start]:18370", "[2,start]:18550", "[3,start]:18940" })]
-    [TestCase("[00:51.00][01:29.99][01:48.29][02:31.00][02:41.99]You gotta fight !", "You gotta fight !", new string[] { "[0,start]:51000" })] // decode with invalid format.
+    [TestCase("[00:51.00][01:29.99][01:48.29][02:31.00][02:41.99]You gotta fight !", "You gotta fight !", new[] { "[0,start]:51000" })] // decode with invalid format.
     [TestCase("帰り道は", "帰り道は", new string[] { })]
     [TestCase("", "", new string[] { })]
     [TestCase(null, "", new string[] { })]
diff --git a/LrcParser/Model/TextIndex.cs b/LrcParser/Model/TextIndex.cs
index d1dfb8a..58bd2d5 100644
--- a/LrcParser/Model/TextIndex.cs
+++ b/LrcParser/Model/TextIndex.cs
@@ -37,7 +37,7 @@ public bool Equals(TextIndex other)
         return Index == other.Index && State == other.State;
     }
 
-    public override bool Equals(object obj)
+    public override bool Equals(object? obj)
     {
         if (obj is TextIndex textIndex)
             return Equals(textIndex);
diff --git a/LrcParser/Parser/Lrc/Lines/LrcRubyParser.cs b/LrcParser/Parser/Lrc/Lines/LrcRubyParser.cs
index 8308bcc..53ef629 100644
--- a/LrcParser/Parser/Lrc/Lines/LrcRubyParser.cs
+++ b/LrcParser/Parser/Lrc/Lines/LrcRubyParser.cs
@@ -45,7 +45,7 @@ public override string Encode(LrcRuby component, int index)
 
         var input = $"@Ruby{index + 1}={parent},{ruby},{startTime},{endTime}";
 
-        const string remove_last_comma_pattern = @"([,]*)$";
+        const string remove_last_comma_pattern = "([,]*)$";
         return Regex.Replace(input, remove_last_comma_pattern, "");
     }
 }
diff --git a/LrcParser/Parser/Lrc/Utils/TimeTagUtils.cs b/LrcParser/Parser/Lrc/Utils/TimeTagUtils.cs
index 7944474..e9d801b 100644
--- a/LrcParser/Parser/Lrc/Utils/TimeTagUtils.cs
+++ b/LrcParser/Parser/Lrc/Utils/TimeTagUtils.cs
@@ -36,6 +36,7 @@ internal static int TimeTagToMillionSecond(string timeTag)
     {
         if (timeTag.Length < 10 || timeTag[0] != '[' || !char.IsDigit(timeTag[1]))
             return -1;
+
         int minute = int.Parse(timeTag.Substring(1, 2));
         int second = int.Parse(timeTag.Substring(4, 2));
         int millionSecond = int.Parse(timeTag.Substring(7, 2));