Warning tells you which function to use instead of rolling_mean. Replace it with Series.rolling. Search online or check in docs to find out how to use it. If you won't be able to get it to work, post again with code and error message.
About removing NaNs or replacing them with another value, it's very easy to find answer to that using your favourite search engine. So again, try it and post back if it won't work.
About removing NaNs or replacing them with another value, it's very easy to find answer to that using your favourite search engine. So again, try it and post back if it won't work.