Index: trunk/Include/Classes/System/Collections/Generic/Dictionary.ab
===================================================================
--- trunk/Include/Classes/System/Collections/Generic/Dictionary.ab	(revision 403)
+++ trunk/Include/Classes/System/Collections/Generic/Dictionary.ab	(revision 410)
@@ -41,7 +41,5 @@
 	Virtual Function Item(key As Key) As T
 		If Object.ReferenceEquals(key, Nothing) Then
-			'Throw ArgumentNullError
-			debug
-			Exit Function
+			Throw New ArgumentNullException("key")
 		End If
 
@@ -60,6 +58,4 @@
 
 		Throw New KeyNotFoundException
-
-		Return Nothing
 	End Function
 
Index: trunk/Include/Classes/System/Collections/Generic/KeyNotFoundException.ab
===================================================================
--- trunk/Include/Classes/System/Collections/Generic/KeyNotFoundException.ab	(revision 403)
+++ trunk/Include/Classes/System/Collections/Generic/KeyNotFoundException.ab	(revision 410)
@@ -1,2 +1,4 @@
+'System/Collections/Generic/KeyNotFoundException.ab
+
 Namespace System
 Namespace Collections
@@ -6,4 +8,29 @@
 Class KeyNotFoundException
 	Inherits System.SystemException
+Public
+	/*!
+	@biref	コンストラクタ
+	*/
+	Sub KeyNotFoundException()
+		SystemException(GetType().FullName, Nothing)
+		HResult = ActiveBasic.AB_E_KEYNOTFOUND
+	End Sub
+	/*!
+	@biref	コンストラクタ
+	@param[in] message	エラーメッセージ
+	*/
+	Sub KeyNotFoundException(message As String)
+		SystemException(message, Nothing)
+		HResult = ActiveBasic.AB_E_KEYNOTFOUND
+	End Sub
+	/*!
+	@biref	コンストラクタ
+	@param[in] message	エラーメッセージ
+	@param[in] innerException	内部例外
+	*/
+	Sub KeyNotFoundException(message As String, innerException As Exception)
+		SystemException(message, innerException)
+		HResult = ActiveBasic.AB_E_KEYNOTFOUND
+	End Sub
 End Class