I've run the adfuller test on my data, and it came out as indicative that there is nowhere near sufficient evidence to reject the null hypothesis. However, I don't even know what the null hypothesis is - is it that there is either a trend or seasonality, or is it just that there is a trend? Since my data is seasonal but doesn't appear to have a trend, I would hope that the former is true, but I don't know. I've looked all over the internet, including, of course, in the documentation, but so far found nothing.
Furthermore, I would also like to confirm that there is indeed seasonality in my data. Would that be possible to do with the adfuller test? If not, how would I test for seasonality?