**Describe the bug** When a property is not defined a `,` is displayed. Then `NaN` **To Reproduce** Steps to reproduce the behavior: 1. Go to 'add-subtract' Examples 2. Click on `+` or `-` 3. See error **Screenshots** If applicable, add screenshots to help explain your problem.  **Additional context** Add any other context about the problem here.
Describe the bug
When a property is not defined a
,is displayed.Then
NaNTo Reproduce
Steps to reproduce the behavior:
+or-Screenshots
If applicable, add screenshots to help explain your problem.
Additional context
Add any other context about the problem here.