diff --git a/Bluehill.Hangul.Pages/Pages/Changelog.razor b/Bluehill.Hangul.Pages/Pages/Changelog.razor
index c0ddc34..96a46ff 100644
--- a/Bluehill.Hangul.Pages/Pages/Changelog.razor
+++ b/Bluehill.Hangul.Pages/Pages/Changelog.razor
@@ -2,6 +2,12 @@
 
 <h2>Changelog</h2>
 
+<h3>2.0.3 (2024-05-02)</h3>
+
+<ol>
+    <li>널 검사 추가</li>
+</ol>
+
 <h3>2.0.2 (2024-05-02)</h3>
 
 <ol>
@@ -114,6 +120,7 @@
 
 <ol>
     <li>문자열이 비어 있을 떄 (<code>""</code>) 조사 처리에 실패하는 문제 수정</li>
+    <li>널 검사 추가</li>
 </ol>
 
 <h3>1.1.1 (2022-11-22)</h3>
diff --git a/Bluehill.Hangul/Bluehill.Hangul.csproj b/Bluehill.Hangul/Bluehill.Hangul.csproj
index 3d1c28d..07278c4 100644
--- a/Bluehill.Hangul/Bluehill.Hangul.csproj
+++ b/Bluehill.Hangul/Bluehill.Hangul.csproj
@@ -5,8 +5,8 @@
     <GeneratePackageOnBuild>True</GeneratePackageOnBuild>
     <Description>한글 관련 라이브러리</Description>
     <AssemblyVersion>2</AssemblyVersion>
-    <FileVersion>2.0.2</FileVersion>
-    <Version>2.0.2</Version>
+    <FileVersion>2.0.3</FileVersion>
+    <Version>2.0.3</Version>
     <SignAssembly>True</SignAssembly>
     <AssemblyOriginatorKeyFile>..\bluehill.snk</AssemblyOriginatorKeyFile>
     <NoWarn>$(NoWarn);0436</NoWarn>
diff --git a/Bluehill.Hangul/CharExtensions.cs b/Bluehill.Hangul/CharExtensions.cs
index b54b68e..3286ca4 100644
--- a/Bluehill.Hangul/CharExtensions.cs
+++ b/Bluehill.Hangul/CharExtensions.cs
@@ -62,4 +62,4 @@ public static class CharExtensions {
     /// <returns><paramref name="hangulSyllable"/>의 초성에 해당하는 <see cref="Hangul.Jongseong"/> 값</returns>
     /// <exception cref="ArgumentException"><paramref name="hangulSyllable"/>가 한글 음절이 아님</exception>
     public static Jongseong Jongseong(this char hangulSyllable) => ((HangulSyllable)hangulSyllable).Jongseong;
-}
\ No newline at end of file
+}
diff --git a/Bluehill.Hangul/Choseong.cs b/Bluehill.Hangul/Choseong.cs
index 97ecf46..21d2218 100644
--- a/Bluehill.Hangul/Choseong.cs
+++ b/Bluehill.Hangul/Choseong.cs
@@ -40,4 +40,4 @@ public enum Choseong : byte {
     Pieup,
     /// <summary>자음 ㅎ을 나타냄</summary>
     Hieut
-}
\ No newline at end of file
+}
diff --git a/Bluehill.Hangul/EnumExtensions.cs b/Bluehill.Hangul/EnumExtensions.cs
index 649dad7..ecc4945 100644
--- a/Bluehill.Hangul/EnumExtensions.cs
+++ b/Bluehill.Hangul/EnumExtensions.cs
@@ -24,4 +24,4 @@ public static class EnumExtensions {
     /// <param name="jongseong"><see cref="Jongseong"/></param>
     /// <returns><paramref name="jongseong"/>에 해당하는 <see cref="char"/> 값</returns>
     public static char ToJamo(this Jongseong jongseong) => Jongseongs[(int)jongseong];
-}
\ No newline at end of file
+}
diff --git a/Bluehill.Hangul/HangulConstants.cs b/Bluehill.Hangul/HangulConstants.cs
index a034b81..bf56065 100644
--- a/Bluehill.Hangul/HangulConstants.cs
+++ b/Bluehill.Hangul/HangulConstants.cs
@@ -168,4 +168,4 @@ public static class HangulConstants {
     /// 유니코드에서 한글 첫가끝 코드 종성의 마지막 문자(ᇂ)를 가리킴
     /// </summary>
     public const char LastIPFJongseong = '\u11C2'; // U+11C2 == 4546 == ᇂ
-}
\ No newline at end of file
+}
diff --git a/Bluehill.Hangul/HangulSyllable.cs b/Bluehill.Hangul/HangulSyllable.cs
index d453653..06bd7ab 100644
--- a/Bluehill.Hangul/HangulSyllable.cs
+++ b/Bluehill.Hangul/HangulSyllable.cs
@@ -16,12 +16,16 @@
     /// </summary>
     public required char Value {
         get {
-            if (!IsValid) throw new InvalidOperationException(invalidMessage);
+            if (!IsValid) {
+                throw new InvalidOperationException(invalidMessage);
+            }
 
             return _Value;
         }
         init {
-            if (!value.IsHangulSyllable()) throw new ArgumentException("문자가 한글 음절 문자가 아닙니다.", nameof(value));
+            if (!value.IsHangulSyllable()) {
+                throw new ArgumentException("문자가 한글 음절 문자가 아닙니다.", nameof(value));
+            }
 
             _Value = value;
         }
@@ -64,7 +68,9 @@ public required char Value {
     /// <exception cref="ArgumentException"><paramref name="c"/>가 한글 음절 문자가 아님</exception>
     [SetsRequiredMembers]
     public HangulSyllable(char c) {
-        if (!c.IsHangulSyllable()) throw new ArgumentException("문자가 한글 음절 문자가 아닙니다.", nameof(c));
+        if (!c.IsHangulSyllable()) {
+            throw new ArgumentException("문자가 한글 음절 문자가 아닙니다.", nameof(c));
+        }
 
         _Value = c;
     }
@@ -87,9 +93,17 @@ public HangulSyllable(char c) {
     /// <exception cref="ArgumentOutOfRangeException">초성 값이 18보다 높을 경우 또는 중성 값이 20보다 높을 경우 또는 종성 값이 27보다 높을 경우</exception>
     [SetsRequiredMembers]
     public HangulSyllable(byte choseong, byte jungseong, byte jongseong) {
-        if (choseong > 18) throw new ArgumentOutOfRangeException(nameof(choseong), choseong, "초성 값은 18 이하여야 합니다.");
-        if (jungseong > 20) throw new ArgumentOutOfRangeException(nameof(jungseong), jungseong, "중성 값은 20 이하여야 합니다.");
-        if (jongseong > 27) throw new ArgumentOutOfRangeException(nameof(jongseong), jongseong, "종성 값은 27 이하여야 합니다.");
+        if (choseong > 18) {
+            throw new ArgumentOutOfRangeException(nameof(choseong), choseong, "초성 값은 18 이하여야 합니다.");
+        }
+
+        if (jungseong > 20) {
+            throw new ArgumentOutOfRangeException(nameof(jungseong), jungseong, "중성 값은 20 이하여야 합니다.");
+        }
+
+        if (jongseong > 27) {
+            throw new ArgumentOutOfRangeException(nameof(jongseong), jongseong, "종성 값은 27 이하여야 합니다.");
+        }
 
         _Value = getChar(choseong, jungseong, jongseong);
     }
@@ -103,9 +117,17 @@ public HangulSyllable(byte choseong, byte jungseong, byte jongseong) {
     /// <exception cref="ArgumentException"><paramref name="choseong"/>이 초성 낱자가 아님 또는 <paramref name="jungseong"/>이 중성 낱자가 아님 또는 <paramref name="jongseong"/>이 종성 낱자가 아님</exception>
     [SetsRequiredMembers]
     public HangulSyllable(char choseong, char jungseong, char jongseong) {
-        if (!Choseongs.Contains(choseong)) throw new ArgumentException("초성 낱자가 아닙니다.", nameof(choseong));
-        if (!Jungseongs.Contains(jungseong)) throw new ArgumentException("중성 낱자가 아닙니다.", nameof(jungseong));
-        if (!Jongseongs.Contains(jongseong)) throw new ArgumentException("종성 낱자가 아닙니다.", nameof(jongseong));
+        if (!Choseongs.Contains(choseong)) {
+            throw new ArgumentException("초성 낱자가 아닙니다.", nameof(choseong));
+        }
+
+        if (!Jungseongs.Contains(jungseong)) {
+            throw new ArgumentException("중성 낱자가 아닙니다.", nameof(jungseong));
+        }
+
+        if (!Jongseongs.Contains(jongseong)) {
+            throw new ArgumentException("종성 낱자가 아닙니다.", nameof(jongseong));
+        }
 
         _Value = getChar(getByte(Choseongs, choseong), getByte(Jungseongs, jungseong), getByte(Jongseongs, jongseong));
 
@@ -204,4 +226,4 @@ public void Deconstruct(out Choseong choseong, out Jungseong jungseong, out Jong
     }
 
     private static char getChar(byte choseong, byte jungseong, byte jongseong) => (char)(FirstSyllable + (((choseong * 21) + jungseong) * 28) + jongseong);
-}
\ No newline at end of file
+}
diff --git a/Bluehill.Hangul/Internal.cs b/Bluehill.Hangul/Internal.cs
index 7e542f8..b03003e 100644
--- a/Bluehill.Hangul/Internal.cs
+++ b/Bluehill.Hangul/Internal.cs
@@ -1,7 +1,7 @@
 namespace Bluehill.Hangul;
 
 internal static class Internal {
-    internal static readonly char[] Choseongs = { 'ㄱ', 'ㄲ', 'ㄴ', 'ㄷ', 'ㄸ', 'ㄹ', 'ㅁ', 'ㅂ', 'ㅃ', 'ㅅ', 'ㅆ', 'ㅇ', 'ㅈ', 'ㅉ', 'ㅊ', 'ㅋ', 'ㅌ', 'ㅍ', 'ㅎ' };
-    internal static readonly char[] Jungseongs = { 'ㅏ', 'ㅐ', 'ㅑ', 'ㅒ', 'ㅓ', 'ㅔ', 'ㅕ', 'ㅖ', 'ㅗ', 'ㅘ', 'ㅙ', 'ㅚ', 'ㅛ', 'ㅜ', 'ㅝ', 'ㅞ', 'ㅟ', 'ㅠ', 'ㅡ', 'ㅢ', 'ㅣ' };
-    internal static readonly char[] Jongseongs = { '\0', 'ㄱ', 'ㄲ', 'ㄳ', 'ㄴ', 'ㄵ', 'ㄶ', 'ㄷ', 'ㄹ', 'ㄺ', 'ㄻ', 'ㄼ', 'ㄽ', 'ㄾ', 'ㄿ', 'ㅀ', 'ㅁ', 'ㅂ', 'ㅄ', 'ㅅ', 'ㅆ', 'ㅇ', 'ㅈ', 'ㅊ', 'ㅋ', 'ㅌ', 'ㅍ', 'ㅎ' };
-}
\ No newline at end of file
+    internal static readonly char[] Choseongs = ['ㄱ', 'ㄲ', 'ㄴ', 'ㄷ', 'ㄸ', 'ㄹ', 'ㅁ', 'ㅂ', 'ㅃ', 'ㅅ', 'ㅆ', 'ㅇ', 'ㅈ', 'ㅉ', 'ㅊ', 'ㅋ', 'ㅌ', 'ㅍ', 'ㅎ'];
+    internal static readonly char[] Jungseongs = ['ㅏ', 'ㅐ', 'ㅑ', 'ㅒ', 'ㅓ', 'ㅔ', 'ㅕ', 'ㅖ', 'ㅗ', 'ㅘ', 'ㅙ', 'ㅚ', 'ㅛ', 'ㅜ', 'ㅝ', 'ㅞ', 'ㅟ', 'ㅠ', 'ㅡ', 'ㅢ', 'ㅣ'];
+    internal static readonly char[] Jongseongs = ['\0', 'ㄱ', 'ㄲ', 'ㄳ', 'ㄴ', 'ㄵ', 'ㄶ', 'ㄷ', 'ㄹ', 'ㄺ', 'ㄻ', 'ㄼ', 'ㄽ', 'ㄾ', 'ㄿ', 'ㅀ', 'ㅁ', 'ㅂ', 'ㅄ', 'ㅅ', 'ㅆ', 'ㅇ', 'ㅈ', 'ㅊ', 'ㅋ', 'ㅌ', 'ㅍ', 'ㅎ'];
+}
diff --git a/Bluehill.Hangul/Jongseong.cs b/Bluehill.Hangul/Jongseong.cs
index 76f4510..9396afb 100644
--- a/Bluehill.Hangul/Jongseong.cs
+++ b/Bluehill.Hangul/Jongseong.cs
@@ -58,4 +58,4 @@ public enum Jongseong : byte {
     Pieup,
     /// <summary>ㅎ 받침을 나타냄</summary>
     Hieut,
-}
\ No newline at end of file
+}
diff --git a/Bluehill.Hangul/Josa.cs b/Bluehill.Hangul/Josa.cs
index a038081..2645dd7 100644
--- a/Bluehill.Hangul/Josa.cs
+++ b/Bluehill.Hangul/Josa.cs
@@ -14,8 +14,24 @@ public static class Josa {
     /// <param name="josaOnly">입력 문자열 없이 조사만 반환할지 여부</param>
     /// <returns>마지막 글자의 받침 여부에 따라 <paramref name="defaultJosa"/> 또는 <paramref name="jongseong"/> 또는 <paramref name="noJongseong"/>을 붙인 문자열</returns>
     public static string Jongseong(this string str, string defaultJosa, string jongseong, string noJongseong, bool josaOnly) {
+        if (str is null) {
+            throw new ArgumentNullException(nameof(str));
+        }
+
+        if (defaultJosa is null) {
+            throw new ArgumentNullException(nameof(defaultJosa));
+        }
+
+        if (jongseong is null) {
+            throw new ArgumentNullException(nameof(jongseong));
+        }
+
+        if (noJongseong is null) {
+            throw new ArgumentNullException(nameof(noJongseong));
+        }
+
         // 문자열이 비어 있으면 기본 조사를 반환
-        if (string.IsNullOrEmpty(str)) {
+        if (str == string.Empty) {
             return defaultJosa;
         }
 
@@ -37,8 +53,24 @@ public static string Jongseong(this string str, string defaultJosa, string jongs
     /// <param name="josaOnly">입력 문자열 없이 조사만 반환할지 여부</param>
     /// <returns>마지막 글자의 ㄹ받침 여부에 따라 <paramref name="defaultJosa"/> 또는 <paramref name="rieul"/> 또는 <paramref name="noRieul"/>을 붙인 문자열</returns>
     public static string NoJongseongOrRieul(this string str, string defaultJosa, string rieul, string noRieul, bool josaOnly) {
+        if (str is null) {
+            throw new ArgumentNullException(nameof(str));
+        }
+
+        if (defaultJosa is null) {
+            throw new ArgumentNullException(nameof(defaultJosa));
+        }
+
+        if (rieul is null) {
+            throw new ArgumentNullException(nameof(rieul));
+        }
+
+        if (noRieul is null) {
+            throw new ArgumentNullException(nameof(noRieul));
+        }
+
         // 문자열이 비어 있으면 기본 조사를 반환
-        if (string.IsNullOrEmpty(str)) {
+        if (str == string.Empty) {
             return defaultJosa;
         }
 
@@ -217,4 +249,4 @@ public static string NoJongseongOrRieul(this string str, string defaultJosa, str
     /// <param name="josaOnly">입력 문자열 없이 조사만 반환할지 여부</param>
     /// <returns>'로' 또는 '으로'를 붙인 문자열</returns>
     public static string EuRo(this string str, string defaultJosa, bool josaOnly) => NoJongseongOrRieul(str, defaultJosa, Ro, Euro, josaOnly);
-}
\ No newline at end of file
+}
diff --git a/Bluehill.Hangul/Jungseong.cs b/Bluehill.Hangul/Jungseong.cs
index c5c6914..e987fc5 100644
--- a/Bluehill.Hangul/Jungseong.cs
+++ b/Bluehill.Hangul/Jungseong.cs
@@ -44,4 +44,4 @@ public enum Jungseong : byte {
     Ui,
     /// <summary>모음 ㅣ를 나타냄</summary>
     I,
-}
\ No newline at end of file
+}