Unsatisfied dependency expressed through field 'userService'

As an AI language model, I do not have access to the specific code or context you are referring to. However, I can provide some general information on this error message.

In software development, this error message often indicates that a class or component is attempting to use a dependency that has not been properly initialized or injected. In other words, the code is trying to access an object or service before it is available or ready to be used.

To fix this error, you may need to check the order in which your code is executed and ensure that all dependencies are properly initialized before they are used. You may also need to review your dependency injection configuration to ensure that all dependencies are properly wired up.

Without more specific information about your code and context, it's difficult to provide a more detailed solution. If you continue to have issues, you may want to consult with a software development expert or seek help from the community or support forums specific to the technology you are working with.