diff --git a/notus/Biblioteque_de_Class/Database.cs b/notus/Biblioteque_de_Class/Database.cs
index e6f641c..d094647 100644
--- a/notus/Biblioteque_de_Class/Database.cs
+++ b/notus/Biblioteque_de_Class/Database.cs
@@ -53,7 +53,7 @@ namespace Biblioteque_de_Class
             {
                 if (logo.GetName() == name) { return logo.GetLogoLink(); }
             }
-            throw new NullReferenceException("No logo link found.");
+            throw new LogoNotFoundException("No logo link found.");
         }
 
         /// <summary>
@@ -68,7 +68,7 @@ namespace Biblioteque_de_Class
                     return user;
                 }
             }
-            throw new NullReferenceException("No user found with this username.");
+            throw new UserAlreadyUsedException("No user found with this username.");
         }
 
         /// <summary>
@@ -103,11 +103,11 @@ namespace Biblioteque_de_Class
             {
                 if (existingUser.GetUsername() == user.GetUsername())
                 {
-                    throw new Exception("Username already used.");
+                    throw new UserAlreadyUsedException("Username already used.");
                 }
                 else if (existingUser.GetEmail() == user.GetEmail())
                 {
-                    throw new Exception("Email already used.");
+                    throw new UserAlreadyUsedException("Email already used.");
                 }
             }
             UserList.Add(user);
@@ -124,7 +124,7 @@ namespace Biblioteque_de_Class
             }
             else
             {
-                throw new NullReferenceException("User not found.");
+                throw new UserNotFoundException("User not found.");
             }
         }
 
@@ -137,7 +137,7 @@ namespace Biblioteque_de_Class
             {
                 if (existingTheme.GetName() == theme.GetName())
                 {
-                    throw new Exception("Theme already used.");
+                    throw new ThemeAlreadyUsedException("Theme already used.");
                 }
             }
             ThemeList.Add(theme);
@@ -154,7 +154,7 @@ namespace Biblioteque_de_Class
             }
             else
             {
-                throw new NullReferenceException("Theme not found.");
+                throw new ThemeNotFoundException("Theme not found.");
             }
         }
 
@@ -170,7 +170,7 @@ namespace Biblioteque_de_Class
                     return theme;
                 }
             }
-            throw new NullReferenceException("No theme found with this name.");
+            throw new ThemeNotFoundException("No theme found with this name.");
         }
 
         /// <summary>
@@ -186,7 +186,7 @@ namespace Biblioteque_de_Class
                     return;
                 }
             }
-            throw new NullReferenceException("Theme not found.");
+            throw new ThemeNotFoundException("Theme not found.");
         }
 
         /// <summary>
@@ -205,7 +205,7 @@ namespace Biblioteque_de_Class
                     return;
                 }
             }
-            throw new NullReferenceException("Theme not found.");
+            throw new ThemeNotFoundException("Theme not found.");
         }
     }
 }
\ No newline at end of file
diff --git a/notus/Biblioteque_de_Class/Exception.cs b/notus/Biblioteque_de_Class/Exception.cs
new file mode 100644
index 0000000..cc1b46c
--- /dev/null
+++ b/notus/Biblioteque_de_Class/Exception.cs
@@ -0,0 +1,33 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Biblioteque_de_Class
+{
+    public class LogoNotFoundException : Exception
+    {
+        public LogoNotFoundException(string message) : base(message)
+        {
+        }
+    }
+    public class UserNotFoundException : Exception
+    {
+        public UserNotFoundException(string message) : base(message)
+        {
+        }
+    }
+    public class ThemeNotFoundException : Exception
+    {
+        public ThemeNotFoundException(string message) : base(message)
+        {
+        }
+    }
+    public class ThemeAlreadyUsedException : Exception
+    {
+        public ThemeAlreadyUsedException(string message) : base(message)
+        {
+        }
+    }
+}