I was able to reproduce the problem you raise, i.e. entering a 'blank' value results in a zero being shown in user-defined graphs. I believe the issue that was fixed in earlier versions, is that some built-in graphs used to have the same bug.
Regardless, the problem is still present in the current version and I will make the development team aware that the problem persists for user-defined graphs.
Thank you for reporting the problem and for your patience,