diff --git a/src/Xamarin.Android.Build.Tasks/Utilities/XAJavaTypeScanner.cs b/src/Xamarin.Android.Build.Tasks/Utilities/XAJavaTypeScanner.cs
index ea863881293..49abcb50c33 100644
--- a/src/Xamarin.Android.Build.Tasks/Utilities/XAJavaTypeScanner.cs
+++ b/src/Xamarin.Android.Build.Tasks/Utilities/XAJavaTypeScanner.cs
@@ -1,3 +1,4 @@
+#nullable enable
 using System;
 using System.Collections.Generic;
 using System.IO;
@@ -90,7 +91,7 @@ bool ShouldScan (ITaskItem assembly)
 		}
 
 		string? hasMonoAndroidReferenceMetadata = assembly.GetMetadata ("HasMonoAndroidReference");
-		if (String.IsNullOrEmpty (hasMonoAndroidReferenceMetadata)) {
+		if (hasMonoAndroidReferenceMetadata.IsNullOrEmpty ()) {
 			return true; // Just in case - the metadata missing might be a false negative
 		}
 
@@ -104,6 +105,11 @@ bool ShouldScan (ITaskItem assembly)
 
 	public void AddJavaType (TypeDefinition type, List<TypeDefinition> types)
 	{
+		if (type == null)
+			throw new ArgumentNullException (nameof (type));
+		if (types == null)
+			throw new ArgumentNullException (nameof (types));
+
 		if (type.HasJavaPeer (cache)) {
 			// For subclasses of e.g. Android.App.Activity.
 			types.Add (type);