account.has_component() does not return boolean

[blais]

Original report by Martin Michlmayr (Bitbucket: tbm13, GitHub: tbm).

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account.has_component() claims to return a boolean:

def has_component(account_name, component):
    """Return true if one of the account contains a given component.

but it doesn't:

from beancount.core import account

a = "Assets:Test:Bar"

print(account.has_component(a, 'Barx'))
print(account.has_component(a, 'Bar'))

results in:

None
<re.Match object; span=(11, 15), match=':Bar'>

I'm not sure if this actually matters in practice but I think the docs should match reality (or vice versa ;)

This can be fixed by adding bool() around the return.

The same problem applies to account.parent_matcher(). Unfortunately I don't know the best way to solve it there.