Null provider message isn't specific

[reubenfirmin]

I'm testing my module using mocks. I'm not supplying a particular property (somewhere). I get the following error message:

com.google.inject.CreationException: Unable to create injector, see the following errors:

1) Binding to null instances is not allowed. Use toProvider(Providers.of(null)) if this is your intended behaviour.
  at com.authzee.kotlinguice4.internal.KotlinBindingBuilder.toInstance(KotlinBindingBuilder.kt)

1 error

Please ensure you are naming the null property in this message, otherwise it's extremely hard to track down.

[johnlcox]

There are no implementations of toInstance in kotlin-guice. All toInstance methods that are part of the kotlin-guice API directly delegate to the Guice implementation of toInstance, which does not add the null property name to the errors.

Unless I'm misunderstanding the issue (a Minimal Complete Verifiable Example would help), this seems like something that would need to be changed in Guice

[reubenfirmin]

Why does it mention a kotlin-guice class (and only that class) in the stack?

You can reproduce this by passing in mocked resources into a module unit test.

[johnlcox]

It looks like Guice uses the method #getElementSource() to get the calling line for toInstance bindings when there are errors.

It might be possible to get a better error message in this case by adding some more exclusions to the error source inclusions like this: https://github.com/authzee/kotlin-guice/blob/master/kotlin-guice/src/main/kotlin/com/authzee/kotlinguice4/KotlinModule.kt#L58

[johnlcox]

Fixed by #13