Add note on NRTs and backing field configuration

entity-framework/core/miscellaneous/nullable-reference-types.md

@@ -32,9 +32,9 @@ Required navigation properties present an additional difficulty: although a depe
 
 One way to deal with these scenarios, is to have a non-nullable property with a nullable [backing field](xref:core/modeling/backing-field):
 
-[!code-csharp[Main](../../../samples/core/Miscellaneous/NullableReferenceTypes/Order.cs?range=12-17)]
+[!code-csharp[Main](../../../samples/core/Miscellaneous/NullableReferenceTypes/Order.cs?range=10-17)]
 
-Since the navigation property is non-nullable, a required navigation is configured; and as long as the navigation is properly loaded, the dependent will be accessible via the property. If, however, the property is accessed without first properly loading the related entity, an InvalidOperationException is thrown, since the API contract has been used incorrectly.
+Since the navigation property is non-nullable, a required navigation is configured; and as long as the navigation is properly loaded, the dependent will be accessible via the property. If, however, the property is accessed without first properly loading the related entity, an InvalidOperationException is thrown, since the API contract has been used incorrectly. Note that EF must be configured to always access the backing field and not the property, as it relies on being able to read the value even when unset; consult the documentation on [backing fields](xref:core/modeling/backing-field) on how to do this, and consider specifying `PropertyAccessMode.Field` to make sure the configuration is correct.
 
 As a terser alternative, it is possible to simply initialize the property to null with the help of the null-forgiving operator (!):