Error Undefined index

I have this error message on several pages of the procurement website.
Does someone know what has to be done to get rid of it?

Thanks a lot.

Dear Isabelle,

It seems that your website is using a custom theme instead of the CERN theme and the error is located in the code of the procurement.theme file.

The person who created the custom theme for your website needs to have a look at it and fix it. We can’t debug this.

Ok! Thanks.