Describe the bug
Donut chart not rendering as expected when the group by variable is a boolean

Powerpipe version (powerpipe -v)
Powerpipe v0.4.0

To reproduce

I am using the below chart definition to create a chart. Howver, it is not producing the expected result.

chart { type = "donut" width = 2 title = "RDS Multi AZ" sql = <<-EOT select multi_az, count(*) from iaws_all.aws_rds_db_instance group by multi_az; EOT }

However, if I use the same chart but on another variable with the value of string type, it produces the expected result.

chart { type = "donut" width = 2 title = "EBS Volume type" sql = <<-EOT select volume_type, count(*) from iaws_all.aws_ebs_volume group by volume_type EOT }

If I change the chart type to bar or column type, it produces the expected result

Expected behavior
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Additional context
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