KB45635: "Error #1009" error message appears when drilling on a graph visualization that is used as a selector of a grid in Visual Insight in MicroStrategy Web 9.4.x

SYMPTOM:
 
In Strategy Web 9.4.x Visual Insight, when a graph is acting as a  selector of a grid, and the user either drills or uses the 'Keep Only' feature, the following error appears. 
 

Error #1009

Error #1009: Cannot access a property or method of a null object reference.

• Create a VI dashboard with the Month and Quarter attributes and the Percent Growth and Profit metrics.
• Add a graph and a grid visualization.
• Have Quarter and both metrics on the graph, and Month and both metrics on the grid.
• Have the graph filter the grid, like shown below: 
  

• Now, attempt to use the "Keep Only" feature or "Drill" from one of the elements in the graph, like shown below. 
  

The error should occur after clicking any of the highlighted options.
 
CAUSE:
This is a known issue in Strategy Web 9.4.0. This occurs as a result of not having the selector attribute shared between the graph and the grid. In the sample above, the graph's selector is Quarter and Quarter is not in the grid visualization.
 
ACTION:
This issue has been addressed with Strategy 10. Upgrade to take advantage of the fix.
 
WORKAROUND:
Follow any of these two options to resolve the issue:

1. Add the selector attribute to the target visualization.
   In the example below, Quarter should be added to the grid.
2. Dismiss the error message by clicking OK. Then click on any data point on the graph; this should refresh the visualization. Then perform the action previously attempted one more time. The action should now occur successfully without showing the error. Alternatively, once the error appears, the user can click the Refresh button on the Strategy Visual Insight toolbar and the previous action that prompted the error message will then be automatically performed, and normal work can continue.