Fix broken integration tests

Author: KoditkarVedant

Test/Notion.IntegrationTests/IPageClientTests.cs

@@ -142,7 +142,7 @@ public async Task Test_RetrievePagePropertyItemAsync()
 
             var listProperty = (ListPropertyItem)property;
 
-            listProperty.Type.Should().BeNull();
+            listProperty.Type.Should().NotBeNull();
             listProperty.Results.Should().SatisfyRespectively(p =>
             {
                 p.Should().BeOfType<TitlePropertyItem>();
@@ -202,7 +202,11 @@ public async Task Test_UpdatePageProperty_with_date_as_null()
 
             var page = await _client.Pages.CreateAsync(pagesCreateParameters);
 
-            var setDate = page.Properties[datePropertyName] as DatePropertyValue;
+            var setDate = (DatePropertyItem)await _client.Pages.RetrievePagePropertyItem(new RetrievePropertyItemParameters
+            {
+                PageId = page.Id,
+                PropertyId = page.Properties[datePropertyName].Id
+            });
 
             setDate?.Date?.Start.Should().Be(Convert.ToDateTime("2020-12-08T12:00:00Z"));
 
@@ -215,7 +219,11 @@ public async Task Test_UpdatePageProperty_with_date_as_null()
                 Properties = testProps
             });
 
-            var verifyDate = updatedPage.Properties[datePropertyName] as DatePropertyValue;
+            var verifyDate = (DatePropertyItem)await _client.Pages.RetrievePagePropertyItem(new RetrievePropertyItemParameters
+            {
+                PageId = page.Id,
+                PropertyId = updatedPage.Properties[datePropertyName].Id
+            });
 
             verifyDate?.Date.Should().BeNull();