чуток поделал

SweetBunsContracts/SweetBunsContracts/Exceptions/ValidationException.cs

@@ -0,0 +1,11 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace SweetBunsContracts.Exceptions;
+
+public class ValidationException(string message) : Exception(message)
+{
+}

SweetBunsContracts/SweetBunsContracts/Extensions/StringExtensions.cs

@@ -0,0 +1,20 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace SweetBunsContracts.Extensions;
+
+public static class StringExtensions
+{
+    public static bool IsEmpty(this string str)
+    {
+        return string.IsNullOrWhiteSpace(str);
+    }
+
+    public static bool IsGuid(this string str)
+    {
+        return Guid.TryParse(str, out _);
+    }
+}

SweetBunsContracts/SweetBunsContracts/Infrastructure/IValidation.cs

@@ -0,0 +1,11 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace SweetBunsContracts.Infrastructure;
+public class IValidation
+{
+    void Validate();
+}

SweetBunsContracts/SweetBunsContracts/SweetBunsContracts.csproj

@@ -6,4 +6,8 @@
     <Nullable>enable</Nullable>
   </PropertyGroup>
 
+  <ItemGroup>
+    <Folder Include="DataModels\" />
+  </ItemGroup>
+
 </Project>