Hidden property doesn't work as expected.

Start with Workbook initialization and the field hidden method referenced in the issue, then run the provided reproduction against CheckBook_2021.2_sql.twb. Compare fields whose XML lacks the hidden attribute with the method's documented return values. Done means the behavior and docstring consistently communicate the intended True/False result, with coverage for fields without the attribute.

Hi. Release 0.10 brought ability to get status of field, either it hidden or not. But in fact Tableau workbook doesn't contain xml attribute for every field, only for hidden. So after initialisation Workbook object if you check fields you will see two values False or None.

But code and docstring inside hidden method tells that as a user I should expect only True False values. Am I right that it's a bug and None values have to be handled?

Code to reproduce:

import tableaudocumentapi
wb = tableaudocumentapi.Workbook('CheckBook_2021.2_sql.twb')
import pandas as pd

fs = []
for s in wb.datasources:
    for k in s.fields:
        try:
            id = s.fields[k].id
        except:
            pass
        try:
            name = s.fields[k].name
        except:
            pass
        try:
            caption = s.fields[k].caption
        except:
            pass
        try:
            calculation = s.fields[k].calculation
        except:
            pass
        try:
            hidden = s.fields[k].hidden
        except:
            pass


        fs.append({'ds': s.caption,
                    'id': id,
                'name': name,
                'caption': caption,
                'calculation': calculation,
                'hidden': hidden
                    })
df = pd.DataFrame.from_records(fs)
df

Result:

CheckBook_2021.2_sql.twb.zip