Invalid info message when boolean field is false

[grv87]

boolean_false.ABOUT file:

about_resource: boolean_false.ABOUT
name: boolean_false
internal_use_only: false

Using develop branch, run:

# about check --verbose boolean_false.ABOUT
Running aboutcode-toolkit version 4.0.0.pre1
Checking ABOUT files...
INFO: about/boolean_false.ABOUT: Field internal_use_only is present but empty.

But field is present and not empty!

I agree with @chinyeungli's #327 (comment):

I think if users put a "No" or false value in the boolean field, they mean to put it there

Related: #326, #327.

[chinyeungli]

Thanks for the report. I will look at this.

[chinyeungli]

For some reasons, the fixes at c6a05b8 are not in the current code.