--- a/mercurial/commands.py	Tue Jun 05 20:47:52 2018 +0200
+++ b/mercurial/commands.py	Thu Aug 23 01:15:19 2018 +0200
@@ -4030,7 +4030,7 @@
     # search for a unique phase argument
     targetphase = None
     for idx, name in enumerate(phases.phasenames):
-        if opts[name]:
+        if opts.get(name, False):
             if targetphase is not None:
                 raise error.Abort(_('only one phase can be specified'))
             targetphase = idx