Разрешил null в моделях бд

Polyclinic/PolyclinicDatabaseImplement/Models/CourseDiagnose.cs

@@ -9,7 +9,7 @@ namespace PolyclinicDatabaseImplement.Models
         public int CourseId { get; set; }
         [Required]
         public int DiagnoseId {  get; set; }
-        public virtual Course Course { get; set; } = new();
-        public virtual Diagnose Diagnose { get; set; } = new();
+        public virtual Course? Course { get; set; }
+        public virtual Diagnose? Diagnose { get; set; }
     }
 }

Polyclinic/PolyclinicDatabaseImplement/Models/Diagnose.cs

@@ -17,7 +17,7 @@ namespace PolyclinicDatabaseImplement.Models
         public DateTime DateStartDiagnose { get; set; } = DateTime.Now;
         public DateTime? DateStopDiagnose { get; set; }
         public int Id { get; set; }
-        public virtual User User { get; set; } = new();
+        public virtual User? User { get; set; }
         
         public static Diagnose? Create(DiagnoseBindingModel? model)
         {

Polyclinic/PolyclinicDatabaseImplement/Models/Procedure.cs

@@ -19,7 +19,7 @@ namespace PolyclinicDatabaseImplement.Models
         [Required]
         public DateTime DateStartProcedure { get; set; } = DateTime.Now;
         public DateTime? DateStopProcedure { get; set; }
-        public virtual User User { get; set; } = new();
+        public virtual User? User { get; set; }
 
         public string? Comment { get; set; } = string.Empty;
 

Polyclinic/PolyclinicDatabaseImplement/Models/RecipeProcedure.cs

@@ -9,7 +9,7 @@ namespace PolyclinicDatabaseImplement.Models
         public int ProcedureId { get; set; }
         [Required]
         public int RecipeId { get; set; }
-        public virtual Procedure Procedure { get; set; } = new();
-        public virtual Recipe Recipe { get; set; } = new();
+        public virtual Procedure? Procedure { get; set; }
+        public virtual Recipe? Recipe { get; set; }
     }
 }

Polyclinic/PolyclinicDatabaseImplement/Models/SymptomDiagnose.cs

@@ -9,7 +9,7 @@ namespace PolyclinicDatabaseImplement.Models
         public int SymptomId { get; set; }
         [Required]
         public int DiagnoseId { get; set; }
-        public virtual Symptom Symptom { get; set; } = new();
-        public virtual Diagnose Diagnose { get; set; } = new();
+        public virtual Symptom? Symptom { get; set; }
+        public virtual Diagnose? Diagnose { get; set; }
     }
 }

Polyclinic/PolyclinicDatabaseImplement/Models/SymptomRecipe.cs

@@ -9,7 +9,7 @@ namespace PolyclinicDatabaseImplement.Models
         public int SymptomId { get; set; }
         [Required]
         public int RecipeId { get; set; }
-        public virtual Symptom Symptom { get; set; } = new();
-        public virtual Recipe Recipe { get; set; } = new();
+        public virtual Symptom? Symptom { get; set; }
+        public virtual Recipe? Recipe { get; set; }
     }
 }