[v6.0.6] Bug: Checkboxes are always being cast to strings despite providing boolean default value.

Describe the bug I’m trying to use react-hook-form with checkboxes and even though the default values for said checkboxes are all booleans (false), as soon as I interact with the checkbox the form value gets cast to a string. I was able to reproduce this fully in the codesandbox below.

To Reproduce

1. Create checkbox components with default values that are booleans
2. watch the values
3. check them and you will see that they are cast to strings.

Codesandbox link (Required) https://codesandbox.io/s/react-hook-form-checkboxes-get-cast-to-strings-everytime-lioo1?file=/src/index.js

Expected behavior I expect the checkboxes to not get cast into strings and simply change from true to false and vice versa.

Screenshots

@bluebill1049 it seems checkbox behaviour also randomly changed, i don’t think I had this problem with older versions but will also double check.

[harrisrobin]

@bluebill1049 I think some improvements to the docs with more checkbox examples and a search feature would help. I’ll take a look at how the docs are setup and see if I can contribute something here.

[bluebill1049]

updated both the doc and CSB to emphasize checkbox example.