fix hash function failing for null property values

src/DynamicObj/HashCodes.fs

@@ -15,7 +15,10 @@ let hashDateTime (dt : System.DateTime) : int =
 
 
 let hash obj =
-    obj.GetHashCode()
+    if obj = null then 
+        0
+    else
+        obj.GetHashCode()
 
 let boxHashOption (a: 'a option) : obj =
     if a.IsSome then a.Value.GetHashCode() else (0).GetHashCode()

tests/DynamicObject.Tests/DynamicObjs.fs

@@ -535,6 +535,21 @@ let tests_GetHashCode = testList "GetHashCode" [
         b2.SetProperty("c", 2)
         a2.SetProperty("b", b2)
         Expect.equal (a.GetHashCode()) (a2.GetHashCode()) "Values should be equal"
+
+    testCase "null Value same key" <| fun _ ->
+        let a = DynamicObj()
+        a.SetProperty("b", null)
+        let b = DynamicObj()
+        b.SetProperty("b", null)
+        Expect.equal (a.GetHashCode()) (b.GetHashCode()) "Values should be equal"
+
+    testCase "null Value different key" <| fun _ ->
+        let a = DynamicObj()
+        a.SetProperty("b", null)
+        let b = DynamicObj()
+        a.SetProperty("c", null)
+        Expect.notEqual (a.GetHashCode()) (b.GetHashCode()) "Values should not be equal"
+
 ]
 
 let main = testList "DynamicObj (Class)" [

tests/DynamicObject.Tests/Inheritance.fs

@@ -68,6 +68,13 @@ let tests_remove = testList "Remove" [
 
         Expect.equal p.FirstName null "Static property should "
 
+    testCase "Remove Static HashCodeDoesNotFail" <| fun _ ->
+        let p = Person("123","John")
+
+        p.RemoveProperty("FirstName") |> ignore
+
+        p.GetHashCode() |> ignore
+
     testCase "Remove Static Immutable" <| fun _ ->
         let p = Person("123","John")
         let f = fun () -> p.RemoveProperty("Id") |> ignore