ISBLANK, NULL or EMPTY in power query
This thing with how Power Query handles nulls, blanks or empty drove me nuts when I was a beginner and still today I manage to forget about it, so here is a video for how to manage them in case you struggle also with it.
Watch the tutorial:
Links to the mentioned resources
In this video, I will show you how to to is blank in power query. If you are trying to do fill down with empties or nulls, check this video instead: