Fatal error: Cannot access empty property

If no fields have (yet) been selected, but the page or block is being called in the browser, the site crashed with a "Fatal error: Cannot access empty property in E:\Programmas\xampp\htdocs\fsl\sites\all\modules\members\members.module on line 1035" (the path will of course differ on someone else's system). Because I enabled a block that was visible site-wide, I had no other choice but to disable the block directly in the database.

This should definitively be fixed, considering it can crash a whole site.