Liquid Exception: 1 is not a symbol nor a string in sitemap.xml

Just fired up Jekyll, and all of sudden I get this error:

Liquid Exception: 1 is not a symbol nor a string in sitemap.xml
jekyll 3.5.0 | Error:  1 is not a symbol nor a string

Things were working fine yesterday, I did not make any changes to any files. Nor did I upgrade anything on my system.

Any idea why that is happening?

Hi, can you post the output of firing Jekyll with an additional --trace switch?

turns out the error is related to this What is this error that I am receiving? was able to fix it following the instructions on github and new sitemap plugin.