добавлние exception

MagicCarpetProject/MagicCarpetContracts/Exceptions/ElementExistsException.cs

@@ -0,0 +1,20 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace MagicCarpetContracts.Exceptions;
+
+public class ElementExistsException : Exception
+{
+    public string ParamName { get; private set; }
+
+    public string ParamValue { get; private set; }
+
+    public ElementExistsException(string paramName, string paramValue) : base($"There is already an element with value{paramValue} of parameter {paramName}")
+    {
+        ParamName = paramName;
+        ParamValue = paramValue;
+    }
+}