TypeError: unsupported operand type for 'NoneType' and 'float'

Hello, I am getting this error in log.

This is the code:

value_template: '{{ 90 - (( as_timestamp(now()) - as_timestamp(strptime(states.sensor.vj_ssl_cert_issued.state, "%Y-%m-%d")) )/ (3600*24)) | round(0) }}'

It seems to work fine in the template editor.