Pie Chart shows duplicate entries for a custom field with multiple Contexts

Summary:

The pie chart shows duplicate entries if you use a custom field as a statistic type with a multiple context containing the same of custom field options.

Steps to Reproduce

1. Create a custom field select list cascading (single option) or Select List (single choice)
2. Configure custom field options
3. Add two or more context for this custom field withe the same custom field options
4. Associate this custom field to a screen
5. Create issues and add a value for this custom field
6. Go to the dashboard and add a gadget "pie chart"
7. Select a filter and use the custom field as the statistic type

Expected Behaviour

No duplicate entries will be shown.

Actual Behaviour

There are duplicate entries on the pie chart gadget probably because of the custom field context configured with the same custom field options.

Workaround

None