> 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/aur0011.md). # AUR0011 Invalid resolver, null/undefined returned from the static register method. ### **Error message** Invalid resolver, null/undefined returned from the static register method. ### Error explanation This error occurs when a static `register` method on a resource or class returns `null` or `undefined` instead of a valid resolver. The DI container expects the `register` method to return a proper resolver object so it can manage the dependency. ### Common causes * The static `register` method does not return anything or returns `null`/`undefined`. * There is a bug or missing return statement in a custom resource or plugin's `register` method. * A plugin or library is not implementing the `register` method correctly. ### How to fix * Ensure that all static `register` methods return a valid resolver object. * Double-check custom resources, plugins, or libraries for correct implementation of the `register` method. * Add appropriate return statements to all `register` methods. ### Debugging tips * Check the stack trace to see which `register` method caused the error. * Search your codebase for all static `register` methods and verify their return values. * If using plugins, try disabling them one at a time to isolate the source. ### Possible solutions Check the static `register` method on the resource/type referenced in the stack trace, and ensure it returns a valid resolver/registration. Please also note that this error could be caused by a plugin and not your application. After ruling out that the error is not being caused by your code, try removing any registered plugins one at a time to see if the error resolves itself. --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation by asking a question. Perform an HTTP GET request on the following URL with the `ask` and `goal` query parameters: ``` GET https://docs.aurelia.io/developer-guides/error-messages/0001-to-0023/aur0011.md?ask=&goal= ``` `ask` is the immediate question: it should be specific, self-contained, and written in natural language. `goal` is what the user is ultimately trying to achieve, the reason they need the answer. Sharing it helps GitBook give you a better, more relevant answer. A goal is most helpful when it describes the outcome the user wants rather than restating the question. For example, with `ask=how do I create an API token`, a goal like `automate deployments from our CI pipeline` lets GitBook tailor the answer to that use case. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.