diff --git a/src/E13.Common.Domain/IDeletable.cs b/src/E13.Common.Domain/IDeletable.cs
index 05dfd76..05d5d8b 100644
--- a/src/E13.Common.Domain/IDeletable.cs
+++ b/src/E13.Common.Domain/IDeletable.cs
@@ -6,7 +6,7 @@ namespace E13.Common.Domain
 {
     public interface IDeletable<T> : IEntity
     {
-        T DeletedBy { get; set; }
+        T? DeletedBy { get; set; }
         string? DeletedSource { get; set; }
         DateTime? Deleted { get; set; }
 
diff --git a/src/E13.Common.Domain/IEffectable.cs b/src/E13.Common.Domain/IEffectable.cs
index 25a28d1..52ecd19 100644
--- a/src/E13.Common.Domain/IEffectable.cs
+++ b/src/E13.Common.Domain/IEffectable.cs
@@ -6,7 +6,7 @@ namespace E13.Common.Domain
 {
     public interface IEffectable<T> : IEntity
     {
-        T EffectiveBy { get; set; }
+        T? EffectiveBy { get; set; }
         string? EffectiveSource { get; set; }
         DateTime? Effective { get; set; }
     }
diff --git a/src/E13.Common.Domain/IExpirable.cs b/src/E13.Common.Domain/IExpirable.cs
index 909181d..f2c3f9a 100644
--- a/src/E13.Common.Domain/IExpirable.cs
+++ b/src/E13.Common.Domain/IExpirable.cs
@@ -6,7 +6,7 @@ namespace E13.Common.Domain
 {
     public interface IExpirable<T> : IEntity
     {
-        T ExpirationBy { get; set; }
+        T? ExpirationBy { get; set; }
         string? ExpirationSource { get; set; }
         DateTime? Expiration { get; set; }
     }
diff --git a/src/E13.Common.Domain/IModifiable.cs b/src/E13.Common.Domain/IModifiable.cs
index 1075ea2..1a425bc 100644
--- a/src/E13.Common.Domain/IModifiable.cs
+++ b/src/E13.Common.Domain/IModifiable.cs
@@ -8,7 +8,7 @@ namespace E13.Common.Domain
 {
     public interface IModifiable<T> : IEntity
     {
-        T ModifiedBy { get; set; }
+        T? ModifiedBy { get; set; }
         string? ModifiedSource { get; set; }
         DateTime? Modified { get; set; }
     }
diff --git a/src/E13.Common.Domain/IOwnable.cs b/src/E13.Common.Domain/IOwnable.cs
index d7041bc..9a7824c 100644
--- a/src/E13.Common.Domain/IOwnable.cs
+++ b/src/E13.Common.Domain/IOwnable.cs
@@ -6,7 +6,7 @@ namespace E13.Common.Domain
 {
     public interface IOwnable<T> : IEntity
     {
-        T OwnedBy { get; set; }
+        T? OwnedBy { get; set; }
         string? OwnedSource { get; set; }
         DateTime? Owned { get; set; }
     }