diff --git a/MCTG/ConsoleApp/Stub.cs b/MCTG/ConsoleApp/Stub.cs
index 87c5a72..a6fc02a 100644
--- a/MCTG/ConsoleApp/Stub.cs
+++ b/MCTG/ConsoleApp/Stub.cs
@@ -18,12 +18,12 @@ namespace ConsoleApp
                 new Recipe("Cookies"),
                 new Recipe("Cookies", 23),
                 new Recipe("Cookies", null),
-                new Recipe(null, null),
-                new Recipe(null, 24),
+                new Recipe("", null),
+                new Recipe("", 24),
                 new Recipe("Cookies", 24,
-                    new PreparationStep(1, null)),
+                    new PreparationStep(1)),
                 new Recipe("Cookies", 26,
-                    new PreparationStep(1, null),
+                    new PreparationStep(1),
                     new PreparationStep(2, "Faire cuire."))
             });
             return stub;
diff --git a/MCTG/Model/PreparationStep.cs b/MCTG/Model/PreparationStep.cs
index 54a9f14..55336d2 100644
--- a/MCTG/Model/PreparationStep.cs
+++ b/MCTG/Model/PreparationStep.cs
@@ -12,7 +12,7 @@ namespace Model
     public class PreparationStep : IEquatable<PreparationStep>
     {
         #region Attributes
-        private string? _description;
+        private string _description = "";
         #endregion
 
         #region Properties
@@ -25,7 +25,7 @@ namespace Model
         /// The description of the task the user need to do for this step of the preparation. <br/>
         /// Set to "No description." when the value passed is null, empty or contain white spaces.
         /// </summary>
-        public string? Description
+        public string Description
         {
             get => _description;
             private set
@@ -44,7 +44,7 @@ namespace Model
         /// </summary>
         /// <param name="order">The number of the order in preparation</param>
         /// <param name="description">The description of the task</param>
-        public PreparationStep(int order, string? description)
+        public PreparationStep(int order, string description = "")
         {
             Order = order;
             Description = description;
@@ -52,8 +52,10 @@ namespace Model
         #endregion
 
         #region Methods
-        public bool Equals(PreparationStep? other)
+        public virtual bool Equals(PreparationStep? other)
         {
+            if (other == null) return false;
+            if (other == this) return true;
             return Order.Equals(other.Order) && Description.Equals(other.Description);
         }
 
diff --git a/MCTG/Model/Recipe.cs b/MCTG/Model/Recipe.cs
index d99da31..8f69fb9 100644
--- a/MCTG/Model/Recipe.cs
+++ b/MCTG/Model/Recipe.cs
@@ -11,9 +11,9 @@ namespace Model
     public class Recipe : IEquatable<Recipe>
     {
         #region Attributes
-        private string? _title;
+        private string _title = "";
         #endregion
-
+
         #region Properties
         /// <summary>
         /// The ID of the recipe - allows you to compare and/or get this item in an easier way.
@@ -24,7 +24,7 @@ namespace Model
         /// The Title of the recipe. <br/>
         /// Set to "No title." when the value passed is null, empty or contain white spaces.
         /// </summary>
-        public string? Title
+        public string Title
         {
             get => _title;
             set
@@ -39,7 +39,7 @@ namespace Model
         /// <summary>
         /// The steps of the preparation. See: <see cref="PreparationStep"/>.
         /// </summary>
-        public List<PreparationStep>? PreparationSteps { get; private set; }
+        public List<PreparationStep> PreparationSteps { get; set; }
         #endregion
 
         #region Constructors
@@ -49,7 +49,7 @@ namespace Model
         /// <param name="title">The title of the recipe</param>
         /// <param name="id">The id of the recipe. If not given, get a new id.</param>
         /// <param name="preparationSteps">The steps of the preparation of the meal</param>
-        public Recipe(string? title = null, int? id = null,
+        public Recipe(string title = "", int? id = null,
                       params PreparationStep[] preparationSteps)
         {
             Title = title;
diff --git a/MCTG/Model/RecipeCollection.cs b/MCTG/Model/RecipeCollection.cs
index 546d2aa..6575729 100644
--- a/MCTG/Model/RecipeCollection.cs
+++ b/MCTG/Model/RecipeCollection.cs
@@ -13,8 +13,8 @@ namespace Model
     public class RecipeCollection : IList<Recipe>, IEquatable<RecipeCollection>
     {
         #region Attributes
-        private readonly List<Recipe> recipes;
-        private string? _description;
+        private readonly List<Recipe> _recipes;
+        private string _description = "";
         #endregion
 
         #region Properties
@@ -22,7 +22,7 @@ namespace Model
         /// A short description of what this collection contain. <br/>
         /// Set to "No description." when the value passed is null, empty or contain white spaces.
         /// </summary>
-        public string? Description
+        public string Description
         {
             get => _description;
             set
@@ -35,21 +35,21 @@ namespace Model
         }
 
         #region IList Prperties
-        public int Count => recipes.Count;
+        public int Count => _recipes.Count;
         public bool IsReadOnly => false;
-        public Recipe this[int index] { get => recipes[index]; set => recipes[index] = value; }
+        public Recipe this[int index] { get => _recipes[index]; set => _recipes[index] = value; }
         #endregion
         #endregion
 
         #region Constructors
         /// <summary>
-        /// Construct a new collection of recipes.
+        /// Construct a new collection of _recipes.
         /// </summary>
         /// <param name="description">A short description of what this list will contain</param>
         /// <param name="recipes">Recipes to add in this new collection</param>
-        public RecipeCollection(string? description = null, params Recipe[] recipes)
+        public RecipeCollection(string description, params Recipe[] recipes)
         {
-            this.recipes = new List<Recipe>(recipes);
+            _recipes = new List<Recipe>(recipes);
             Description = description;
         }
         #endregion
@@ -63,79 +63,80 @@ namespace Model
         /// <exception cref="ArgumentException"/>
         public Recipe? GetRecipeById(int id)
         {
-            Recipe? recipe = recipes.Find(r => r.Id == id);
-            if (recipe == null) throw new ArgumentException("No recipes match the given id.");
+            Recipe? recipe = _recipes.Find(r => r.Id == id);
+            if (recipe == null) throw new ArgumentException("No _recipes match the given id.");
             return recipe;
         }
 
         #region IList Methods
         public int IndexOf(Recipe item)
         {
-            return recipes.IndexOf(item);
+            return _recipes.IndexOf(item);
         }
 
         public void Insert(int index, Recipe item)
         {
-            recipes.Insert(index, item);
+            _recipes.Insert(index, item);
         }
 
         public void RemoveAt(int index)
         {
-            recipes.RemoveAt(index);
+            _recipes.RemoveAt(index);
         }
 
         public void Add(Recipe item)
         {
-            recipes.Add(item);
+            _recipes.Add(item);
         }
 
         public void Clear()
         {
-            recipes.Clear();
+            _recipes.Clear();
         }
 
         public bool Contains(Recipe item)
         {
-            return recipes.Contains(item);
+            return _recipes.Contains(item);
         }
 
         public void CopyTo(Recipe[] array, int arrayIndex)
         {
-            recipes.CopyTo(array, arrayIndex);
+            _recipes.CopyTo(array, arrayIndex);
         }
 
         public bool Remove(Recipe item)
         {
-            return recipes.Remove(item);
+            return _recipes.Remove(item);
         }
 
         public IEnumerator<Recipe> GetEnumerator()
         {
-            return recipes.GetEnumerator();
+            return _recipes.GetEnumerator();
         }
 
         IEnumerator IEnumerable.GetEnumerator()
         {
-            return recipes.GetEnumerator();
+            return _recipes.GetEnumerator();
         }
         #endregion
 
         public virtual bool Equals(RecipeCollection? other)
         {
+            
             if (other == null) return false;
             if (other == this) return true;
-            return Description.Equals(other.Description) && recipes.Equals(other.recipes);
+            return _description.Equals(other.Description) && _recipes.Equals(other._recipes);
         }
 
         public override int GetHashCode()
         {
-            return recipes.GetHashCode();
+            return _recipes.GetHashCode();
         }
 
         public override string ToString()
         {
             StringBuilder sb = new StringBuilder($"[RecipeCollection] - {Description}:\n");
-            foreach (Recipe r in recipes)
+            foreach (Recipe r in _recipes)
             {
                 sb.AppendFormat("\t - {0}\n", r.ToString());
             }
diff --git a/MCTG/Tests/Model_UnitTests/Recipe_UT.cs b/MCTG/Tests/Model_UnitTests/Recipe_UT.cs
index 55df465..e8593a5 100644
--- a/MCTG/Tests/Model_UnitTests/Recipe_UT.cs
+++ b/MCTG/Tests/Model_UnitTests/Recipe_UT.cs
@@ -15,7 +15,6 @@ namespace Model_UnitTests
         [InlineData("Cookies", 23, "Cookies", 23)]
         [InlineData("Cookies", 1, "Cookies", 1)]
         [InlineData("No title.", 1, "", 1)]
-        [InlineData("No title.", 1, null, 1)]
         public void TestConstructor(string expectedTitle, int expectedId, string title, int? id)
         {
             Recipe r = new Recipe(title, id);