Bug#621006: lintian: Variable substitution in "Maintainer" field in causes warnings and "no-maintainer-field" error

[Dmitry Katsubo <dma_k@mail.ru>]

Package: lintian
Version: 2.4.3

When debian/control file reads:

=== cut ===
Maintainer: ${common:Maintainer}
=== cut ===

and in my debian/substvars I have:

=== cut ===
common:Maintainer=Dmitry Katsubo <dma_k@mail.ru>
=== cut ===

the lintian produces the following warnings for "osra source" package
and "no-maintainer-field" error (but reports nothing for other "real"
packages):

> Now running lintian...
> Use of uninitialized value $maintainer in substitution (s///) at /usr/share/lintian/checks/nmu line 139.
> Use of uninitialized value $maintainer in string ne at /usr/share/lintian/checks/nmu line 97.
> Use of uninitialized value $maintainer in pattern match (m//) at /usr/share/lintian/checks/nmu line 109.
> E: osra source: no-maintainer-field

Expected: the maintainer field is analysed with respect to variable
substitution.