Visualizations display "0" and "1" for boolean fields with a static lookup formatter

[n0othing]

Kibana version: 7.13

Elasticsearch version: 7.13

Describe the bug:

Visualizations display "0" and "1" for boolean fields with a static lookup formatter. Classic Visualize's pie chart behaves extra weird.

Steps to reproduce:

1. Create an index with a boolean data type

   PUT index
   {
   "mappings": {
   "properties": {
     "boolean_field": {
       "type": "boolean"
     }
   }
   }
   }

   
   POST index/_doc?refresh
   {
   "boolean_field": true
   }

POST index/_doc?refresh { "boolean_field": false }

2. Add `index` as an index pattern in Kibana
3. Apply a Static Lookup field formatter like so:
![static_lookup](https://user-images.githubusercontent.com/11917935/119900148-19513100-bf12-11eb-83e0-8d35191c1c13.jpg)
4. Build a Visualize > Pie Chart, performing a terms agg on `boolean_field`. The pie chart shows `0` and `1` in the legend and the chart goes black. Similar behavior in Lens (but colors don't go black). Removing the formatter makes things behave normally (e.g the legend displays `true` and `false`).

**Screenshots (if relevant):**

![pie_chart](https://user-images.githubusercontent.com/11917935/119900434-849b0300-bf12-11eb-8c9c-a6d1b53921f5.jpg)

![Lens_boolean](https://user-images.githubusercontent.com/11917935/119900554-ad22fd00-bf12-11eb-875f-ee019ea0b66f.jpg)

[elasticmachine]

Pinging @elastic/kibana-app (Team:KibanaApp)

[flash1293]

This is a bug in field formatters, not visualizations. I agree that true and false mapping should work as implied in the description.

[heysulo]

any update on this?

[elasticmachine]

Pinging @elastic/kibana-data-discovery (Team:DataDiscovery)

[beningodfrey4]

For anyone still encountering this issue, a workaround is to create a scripted field of "Type: number" and "Format: Static Lookup".

Add entries for 0 and 1 mapping to the string you want for false and true correspondingly.

Then the script can just be return params._source.<original_bool_field>.