pullrequests: simplify handling of null revisions

Undo unnecessary and incorrect code introduced in bd5420ea396b.

rhodecode/model/pull_request.py

@@ -39,7 +39,6 b' from rhodecode.lib.utils2 import safe_un'
 
 from rhodecode.lib.vcs.utils.hgcompat import scmutil
 from rhodecode.lib.vcs.utils import safe_str
-from rhodecode.lib.vcs.backends.base import EmptyChangeset
 
 log = logging.getLogger(__name__)
 
@@ -186,16 +185,11 b' class PullRequestModel(BaseModel):'
 
             org_rev_spec = "%s('%s')" % (_revset_predicates[org_ref[0]],
                                          safe_str(org_ref[1]))
-            if org_ref[1] == EmptyChangeset().raw_id:
-                org_rev = org_ref[1]
-            else:
                 org_rev = org_repo._repo[scmutil.revrange(org_repo._repo,
                                                           [org_rev_spec])[-1]]
+
             other_rev_spec = "%s('%s')" % (_revset_predicates[other_ref[0]],
                                            safe_str(other_ref[1]))
-            if other_ref[1] == EmptyChangeset().raw_id:
-                other_rev = other_ref[1]
-            else:
                 other_rev = other_repo._repo[scmutil.revrange(other_repo._repo,
                                                         [other_rev_spec])[-1]]