py3: replace str(None) with literal in convcmd.py

hgext/convert/convcmd.py

@@ -87,7 +87,7 b' def mapbranch(branch, branchmap):'
     # At some point we used "None" literal to denote the default branch,
     # attempt to use that for backward compatibility.
     if (not branch):
-        branch = branchmap.get(str(None), branch)
+        branch = branchmap.get('None', branch)
     return branch
 
 source_converters = [

tests/test-doctest.py

@@ -71,7 +71,7 b" testmod('mercurial.ui')"
 testmod('mercurial.url')
 testmod('mercurial.util', py3=False)  # py3: multiple bytes/unicode issues
 testmod('mercurial.util', testtarget='platform')
-testmod('hgext.convert.convcmd', py3=False)  # py3: use of str() ?
+testmod('hgext.convert.convcmd')
 testmod('hgext.convert.cvsps')
 testmod('hgext.convert.filemap')
 testmod('hgext.convert.p4')