diff -r 7546bf46bfcd -r 0bd730fbcc2b mercurial/branchmap.py
--- a/mercurial/branchmap.py	Mon Mar 18 19:11:55 2019 +0300
+++ b/mercurial/branchmap.py	Mon Mar 18 19:31:45 2019 +0300
@@ -175,6 +175,10 @@
     def iteritems(self):
         return self.entries.iteritems()
 
+    def hasbranch(self, label):
+        """ checks whether a branch of this name exists or not """
+        return label in self.entries
+
     @classmethod
     def fromfile(cls, repo):
         f = None