diff --git a/src/WebKit/DomCssRuleList.cs b/src/WebKit/DomCssRuleList.cs
index 1019bf8ab5ef..adc06211e36c 100644
--- a/src/WebKit/DomCssRuleList.cs
+++ b/src/WebKit/DomCssRuleList.cs
@@ -1,3 +1,5 @@
+#nullable enable
+
 namespace WebKit {
 	
 	public partial class DomCssRuleList {
diff --git a/src/WebKit/DomHelpers.cs b/src/WebKit/DomHelpers.cs
index ead1b62e27b2..cbfea7c810d2 100644
--- a/src/WebKit/DomHelpers.cs
+++ b/src/WebKit/DomHelpers.cs
@@ -1,3 +1,5 @@
+#nullable enable
+
 using System;
 using ObjCRuntime;
 using Foundation;
diff --git a/src/WebKit/DomNode.cs b/src/WebKit/DomNode.cs
index 3ea8d94f86e8..fd4122757598 100644
--- a/src/WebKit/DomNode.cs
+++ b/src/WebKit/DomNode.cs
@@ -21,6 +21,8 @@
 // WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 //
 
+#nullable enable
+
 using System;
 using System.Runtime.Versioning;
 
@@ -77,8 +79,8 @@ public IDomEventListener AddEventListener (string type, DomEventListenerHandler
 		public DomEventListener AddEventListener (string type, DomEventListenerHandler handler, bool useCapture)
 #endif
 		{
-			if (handler == null)
-				throw new ArgumentNullException ("handler");
+			if (handler is null)
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (handler));
 			var obj = new DomNodeEventProxy (this, handler);
 			AddEventListener (type, obj, useCapture);
 			return obj;
@@ -90,8 +92,8 @@ public IDomEventListener AddEventListener (string type, Action<DomEvent> callbac
 		public DomEventListener AddEventListener (string type, Action<DomEvent> callback, bool useCapture)
 #endif
 		{
-			if (callback == null)
-				throw new ArgumentNullException ("callback");
+			if (callback is null)
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (callback));
 			var obj = new DomNodeEventProxy2 (callback);
 			AddEventListener (type, obj, useCapture);
 			return obj;
diff --git a/src/WebKit/Enumerators.cs b/src/WebKit/Enumerators.cs
index 144586be2875..88b99218c091 100644
--- a/src/WebKit/Enumerators.cs
+++ b/src/WebKit/Enumerators.cs
@@ -1,3 +1,5 @@
+#nullable enable
+
 using System;
 using System.Collections;
 using System.Collections.Generic;
@@ -24,15 +26,19 @@ public void Dispose () {
 
 		public T Current {
 			get {
+				if (_container is null)
+					throw new ObjectDisposedException (nameof (_container));
 				return _container [_index];
 			}
 		}
 
-		object IEnumerator.Current {
+		object? IEnumerator.Current {
 			get { return ((IEnumerator<T>) this).Current; }
 		}
 
 		public bool MoveNext () {
+			if (_container is null)
+				throw new ObjectDisposedException (nameof (_container));
 			return ++_index < _container.Count;
 		}
 
@@ -40,7 +46,7 @@ public void Reset () {
 			_index = -1;
 		}
 
-		IIndexedContainer<T> _container;
+		IIndexedContainer<T>? _container;
 		int _index;
 	}
 
diff --git a/src/WebKit/Indexers.cs b/src/WebKit/Indexers.cs
index a6d935ecc2f9..2e9f038015e4 100644
--- a/src/WebKit/Indexers.cs
+++ b/src/WebKit/Indexers.cs
@@ -1,3 +1,5 @@
+#nullable enable
+
 namespace WebKit {
 	
 	public partial class DomCssRuleList {
diff --git a/src/WebKit/WebKit.cs b/src/WebKit/WebKit.cs
index bdba3eed9467..3ddcce6e4854 100644
--- a/src/WebKit/WebKit.cs
+++ b/src/WebKit/WebKit.cs
@@ -1,3 +1,5 @@
+#nullable enable
+
 using Foundation;
 
 namespace WebKit {
diff --git a/src/WebKit/WebNavigationPolicyEventArgs.cs b/src/WebKit/WebNavigationPolicyEventArgs.cs
index f413d5044c58..21a4bd4b9bcf 100644
--- a/src/WebKit/WebNavigationPolicyEventArgs.cs
+++ b/src/WebKit/WebNavigationPolicyEventArgs.cs
@@ -6,6 +6,8 @@
 //
 // Copyright 2013 Xamarin Inc
 
+#nullable enable
+
 using System;
 
 using Foundation;
@@ -27,14 +29,14 @@ public WebNavigationType NavigationType {
 			get { return (WebNavigationType)((NSNumber)ActionInformation[WebPolicyDelegate.WebActionNavigationTypeKey]).Int32Value; }
 		}
 
-		public NSDictionary ElementInfo {
+		public NSDictionary? ElementInfo {
 			get { return ActionInformation[WebPolicyDelegate.WebActionElementKey] as NSDictionary; }
 		}
 
 		public WebActionMouseButton MouseButton {
 			get {
 				var number = ActionInformation[WebPolicyDelegate.WebActionButtonKey] as NSNumber;
-				if (number == null) {
+				if (number is null) {
 					return WebActionMouseButton.None;
 				}
 
@@ -46,7 +48,7 @@ public uint Flags {
 			get { return ((NSNumber)ActionInformation[WebPolicyDelegate.WebActionModifierFlagsKey]).UInt32Value; }
 		}
 
-		public NSUrl OriginalUrl {
+		public NSUrl? OriginalUrl {
 			get { return ActionInformation[WebPolicyDelegate.WebActionOriginalUrlKey] as NSUrl; }
 		}
 	}
diff --git a/src/WebKit/WebPolicyDelegate.cs b/src/WebKit/WebPolicyDelegate.cs
index d97e8e7c8b21..4058862bf534 100644
--- a/src/WebKit/WebPolicyDelegate.cs
+++ b/src/WebKit/WebPolicyDelegate.cs
@@ -20,6 +20,9 @@
 // OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
 // WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 //
+
+#nullable enable
+
 using System;
 using Foundation;
 using ObjCRuntime;
@@ -33,24 +36,24 @@ public partial class WebPolicyDelegate {
 		
 		public static void DecideUse (NSObject decisionToken)
 		{
-			if (decisionToken == null)
-				throw new ArgumentNullException ("token");
+			if (decisionToken is null)
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (decisionToken));
 			
 			ObjCRuntime.Messaging.void_objc_msgSend (decisionToken.Handle, selUse);
 		}
 		
 		public static void DecideDownload (NSObject decisionToken)
 		{
-			if (decisionToken == null)
-				throw new ArgumentNullException ("decisionToken");
+			if (decisionToken is null)
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (decisionToken));
 			
 			ObjCRuntime.Messaging.void_objc_msgSend (decisionToken.Handle, selDownload);
 		}
 		
 		public static void DecideIgnore (NSObject decisionToken)
 		{
-			if (decisionToken == null)
-				throw new ArgumentNullException ("decisionToken");
+			if (decisionToken is null)
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (decisionToken));
 			
 			ObjCRuntime.Messaging.void_objc_msgSend (decisionToken.Handle, selIgnore);
 		}
diff --git a/src/WebKit/WebView.cs b/src/WebKit/WebView.cs
index c388ba8d9e97..303c8147d156 100644
--- a/src/WebKit/WebView.cs
+++ b/src/WebKit/WebView.cs
@@ -20,6 +20,9 @@
 // OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
 // WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 //
+
+#nullable enable
+
 using System;
 using Foundation;
 using ObjCRuntime;
@@ -33,24 +36,24 @@ public partial class WebView {
 		
 		public static void DecideUse (NSObject decisionToken)
 		{
-			if (decisionToken == null)
-				throw new ArgumentNullException ("token");
+			if (decisionToken is null)
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (decisionToken));
 			
 			ObjCRuntime.Messaging.void_objc_msgSend (decisionToken.Handle, selUse);
 		}
 		
 		public static void DecideDownload (NSObject decisionToken)
 		{
-			if (decisionToken == null)
-				throw new ArgumentNullException ("decisionToken");
+			if (decisionToken is null)
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (decisionToken));
 			
 			ObjCRuntime.Messaging.void_objc_msgSend (decisionToken.Handle, selDownload);
 		}
 		
 		public static void DecideIgnore (NSObject decisionToken)
 		{
-			if (decisionToken == null)
-				throw new ArgumentNullException ("decisionToken");
+			if (decisionToken is null)
+				ObjCRuntime.ThrowHelper.ThrowArgumentNullException (nameof (decisionToken));
 			
 			ObjCRuntime.Messaging.void_objc_msgSend (decisionToken.Handle, selIgnore);
 		}