diff --git a/src/InternshipSystem.Api/InternshipSystem.Api.csproj b/src/InternshipSystem.Api/InternshipSystem.Api.csproj
index e084254..1252f96 100644
--- a/src/InternshipSystem.Api/InternshipSystem.Api.csproj
+++ b/src/InternshipSystem.Api/InternshipSystem.Api.csproj
@@ -4,6 +4,7 @@
     <TargetFramework>netcoreapp3.1</TargetFramework>
     <GenerateDocumentationFile>true</GenerateDocumentationFile>
     <LangVersion>latest</LangVersion>
+    <NoWarn>$(NoWarn);1591;1573</NoWarn>
   </PropertyGroup>
 
   <ItemGroup>
@@ -16,10 +17,6 @@
     <PackageReference Include="IdentityServer4" Version="3.1.4" />
   </ItemGroup>
 
-  <ItemGroup>
-    <Folder Include="Controllers" />
-  </ItemGroup>
-
   <ItemGroup>
     <ProjectReference Include="../InternshipSystem.Core/InternshipSystem.Core.csproj" />
     <ProjectReference Include="../InternshipSystem.Repository/InternshipSystem.Repository.csproj" />
diff --git a/src/InternshipSystem.Core/Entity/Company.cs b/src/InternshipSystem.Core/Entity/Company.cs
index 6b98e0f..ddbeeb4 100644
--- a/src/InternshipSystem.Core/Entity/Company.cs
+++ b/src/InternshipSystem.Core/Entity/Company.cs
@@ -6,7 +6,7 @@ namespace InternshipSystem.Core
     public class Company
     {
         public long Id { get; set; }
-        public string Nip { get; set; }
+        public Nip Nip { get; set; }
         public string Name { get; set; }
         public RangeOfActivity Range { get; set; }
         public List<BranchOffice> Branches { get; set; }
diff --git a/src/InternshipSystem.Core/ValueObject/Mentor.cs b/src/InternshipSystem.Core/ValueObject/Mentor.cs
index d7be213..4af5c24 100644
--- a/src/InternshipSystem.Core/ValueObject/Mentor.cs
+++ b/src/InternshipSystem.Core/ValueObject/Mentor.cs
@@ -5,6 +5,6 @@
         public string FirstName { get; set; }
         public string LastName { get; set; }
         public string Email { get; set; }
-        public string PhoneNumber { get; set; }
+        public PhoneNumber PhoneNumber { get; set; }
     }
 }
\ No newline at end of file
diff --git a/src/InternshipSystem.Core/ValueObject/Nip.cs b/src/InternshipSystem.Core/ValueObject/Nip.cs
new file mode 100644
index 0000000..903b59e
--- /dev/null
+++ b/src/InternshipSystem.Core/ValueObject/Nip.cs
@@ -0,0 +1,18 @@
+namespace InternshipSystem.Core
+{
+    public struct Nip
+    {
+        private readonly string _nip;
+
+        public Nip(string nip)
+        {
+            _nip = nip;
+        }
+
+        public static implicit operator string(Nip nip) =>
+            nip._nip;
+        
+        public static implicit operator Nip(string maybeNip) =>
+            new Nip(maybeNip);
+    }
+}
\ No newline at end of file
diff --git a/src/InternshipSystem.Core/ValueObject/PhoneNumber.cs b/src/InternshipSystem.Core/ValueObject/PhoneNumber.cs
new file mode 100644
index 0000000..e72d355
--- /dev/null
+++ b/src/InternshipSystem.Core/ValueObject/PhoneNumber.cs
@@ -0,0 +1,18 @@
+namespace InternshipSystem.Core
+{
+    public struct PhoneNumber
+    {
+        private readonly string _phoneNumber;
+
+        public PhoneNumber(string phoneNumber)
+        {
+            _phoneNumber = phoneNumber;
+        }
+
+        public static implicit operator string(PhoneNumber number) =>
+            number._phoneNumber;
+        
+        public static implicit operator PhoneNumber(string maybeNumber) =>
+            new PhoneNumber(maybeNumber);
+    }
+}
\ No newline at end of file
diff --git a/src/InternshipSystem.Repository/InternshipDbContext.cs b/src/InternshipSystem.Repository/InternshipDbContext.cs
index 83ed627..716aef9 100644
--- a/src/InternshipSystem.Repository/InternshipDbContext.cs
+++ b/src/InternshipSystem.Repository/InternshipDbContext.cs
@@ -21,11 +21,21 @@ namespace InternshipSystem.Repository
 
         protected override void OnModelCreating(ModelBuilder modelBuilder)
         {
+            modelBuilder.Entity<Company>()
+                .Property(company => company.Nip)
+                .HasConversion<string>(
+                    nip => nip,
+                    s => (Nip)s);
+
             modelBuilder.Entity<BranchOffice>()
                 .OwnsOne(bo => bo.Address);
 
             modelBuilder.Entity<InternshipProgram>()
-                .OwnsOne(ip => ip.Mentor);
+                .OwnsOne(ip => ip.Mentor)
+                .Property(mentor => mentor.PhoneNumber)
+                .HasConversion<string>(
+                    number => number,
+                    s => (PhoneNumber)s);
 
             modelBuilder.Entity<ProgramSubject>(builder =>
             {