> For the complete documentation index, see [llms.txt](https://docs.aurelia.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.aurelia.io/developer-guides/error-messages/0001-to-0023/aur0004.md).

# AUR0004

Resolver for yyyy returned a null factory

### **Error message**

Resolver for `yyyy` returned a null factory

### **Parameters**

String version of the key being resolved

### Error explanation

This error occurs when the DI container tries to resolve a transient registration, but no factory was found for the given key. A factory is required to create new instances for transients, and if it is missing or not properly registered, this error will be thrown.

### Common causes

* You registered a transient dependency without providing a factory.
* The factory for the key was not registered correctly or was accidentally removed.
* There is a typo or mismatch in the key used for registration and resolution.
* A plugin or library expected to register the factory did not do so.

### How to fix

* Register a factory for the key using `container.registerFactory(IMyInterface, someFactoryObject)`.
* Double-check that the key used for registration matches the key used for resolution.
* Ensure that any plugins or libraries you are using are properly configured and registered.

### Debugging tips

* Check the stack trace to see where the resolution was attempted.
* Search your codebase for all registrations and resolutions of the key in question.
* If using plugins, try disabling them one at a time to isolate the source.


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