context: explicitly tests for None

context: explicitly tests for None

Changeset 9e57033fec0c removed the mutable default value, but did not explicitly
tested for None. Such implicit testing can introduce semantic and performance
issue. We move to an explicit testing for None as recommended by PEP8:

https://www.python.org/dev/peps/pep-0008/#programming-recommendations

--- a/mercurial/context.py	Wed Mar 15 15:11:52 2017 -0700
+++ b/mercurial/context.py	Wed Mar 15 15:33:24 2017 -0700
@@ -300,8 +300,10 @@
 
     def match(self, pats=None, include=None, exclude=None, default='glob',
               listsubrepos=False, badfn=None):
+        if pats is None:
+            pats = []
         r = self._repo
-        return matchmod.match(r.root, r.getcwd(), pats or [],
+        return matchmod.match(r.root, r.getcwd(), pats,
                               include, exclude, default,
                               auditor=r.nofsauditor, ctx=self,
                               listsubrepos=listsubrepos, badfn=badfn)
@@ -1517,16 +1519,18 @@
 
     def match(self, pats=None, include=None, exclude=None, default='glob',
               listsubrepos=False, badfn=None):
+        if pats is None:
+            pats = []
         r = self._repo
 
         # Only a case insensitive filesystem needs magic to translate user input
         # to actual case in the filesystem.
         if not util.fscasesensitive(r.root):
-            return matchmod.icasefsmatcher(r.root, r.getcwd(), pats or [],
+            return matchmod.icasefsmatcher(r.root, r.getcwd(), pats,
                                            include, exclude, default, r.auditor,
                                            self, listsubrepos=listsubrepos,
                                            badfn=badfn)
-        return matchmod.match(r.root, r.getcwd(), pats or [],
+        return matchmod.match(r.root, r.getcwd(), pats,
                               include, exclude, default,
                               auditor=r.auditor, ctx=self,
                               listsubrepos=listsubrepos, badfn=badfn)