(rename is not always straightforward!):
When you rename a topic, you may be able to ask (depending on how this site is configured) to have references to the topic automatically updated.
References from other namespaces are not updated
Plural references are not found
Because not all references can be reliably found (e.g., because a topic has been bookmarked by someone, or is referenced from another namespace), a page will be automatically generated that tells people where the new page is.
Often when you rename a topic you are changing its meaning. As a result, you might want to change the text surrounding the references to the topic; please consider reviewing the current references when you are done renaming to be sure they still make sense.
Automatically update references
Generate a redirect page under the old name
Object reference not set to an instance of an object.