Are you using a template for your home page? If your home page is based on a page template that contains a language selector control then it throws this exception. Please, tell me if you are setting your home page in a similar way.
I can reproduce this issue following the steps below and there is a bug logged for this scenario.
1. Enable multilingual mode with two languages
2. Create a template with a language selector control
3. Create a page using this template and set this page as a home page
4. Navigate to the project and "Object reference not set to an instance of an object" error is thrown
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