Hey, it is St. Patrick's Day

After spending who knows how long writing and reviewing something, small errors like this can be missed because your brain is hyper aware of what you meant, and automatically corrects it as you read. Meaning you think you did things right until you take a break and come back to it, which isn't an option in some cases, like when the document you are writing is an apology for your already troubling lack of communication.

It's a spelling mistake everyone makes them you don't need to find an excuse for it.

Not to mention it's spelled "absence" in the US as well.