NullReferenceException thrown during context.AddError when failing to CompleteCompositeType

[tunurgitr]

Describe the bug
When executing a query with a schema defined by an interface with implementations registered, an error is thrown within the error reporting infrastructure.

To Reproduce
Steps to reproduce the behavior:

1. Define a code-first interface, but don't add the implementation types
2. Try to do a query that maps these interfaces

Expected behavior
A helpful error would be thrown indicating there was a problem mapping the CLR class to a registered type.

Additional context
https://github.com/ChilliCream/hotchocolate/blob/89b0a5d97a500e7fd6d16856987e417f524c6e42/src/Core/Core/Execution/Utilities/ValueCompletion.cs#L179

context.Value is null. Seems like it should be using the name of type.

[michaelstaib]

I think the main issue here is that we create the schema in the first place since it is inconsistent.... let me check the spec first.

[michaelstaib]

OK, this is now fixed.

[michaelstaib]

So,

I have fixed also the execution engine code .... the context.Value was wrong in any way since that is the coerced output value. The type should be extracted from the result argument.

But I also added more context here.... the new error message is:

Could not resolve the actual object type from `System.String` for the abstract type `Bar`.

Apart from that the schema now validates interfaces more strict.

If you are in porto typing mode you can opt-out of the strictness with

SchemaBuilder
     ....
     .ModifyOption(o => o.StrictValidation = false)
     .Create()