[PATCH 4 of 4 accept-scripts] land: fix JSON error when no accepted changes to land

[Kevin Bullock]

# HG changeset patch
# User Kevin Bullock <kbullock at ringworld.org>
# Date 1525292842 18000
#      Wed May 02 15:27:22 2018 -0500
# Node ID bafcc443cd52382c574822bd4fef2f83141b10e1
# Parent  335d45810dd93321242e7c329cf6d603a3aa7516
land: fix JSON error when no accepted changes to land

diff --git a/land b/land
--- a/land
+++ b/land
@@ -50,6 +50,9 @@ all_accepted = [n for n in cq.draft() if
 acceptrange = collections.namedtuple('acceptrange', 'roots head')
 
 def accepted_ranges(all_accepted):
+    if not all_accepted:
+        return []
+
     accepted_revset = ' + '.join(all_accepted)
     info = json.load(os.popen("hg log -R %s -r '%s' -Tjson" % (
         conf.source, accepted_revset)))
diff --git a/tests/test-land.t b/tests/test-land.t
--- a/tests/test-land.t
+++ b/tests/test-land.t
@@ -1,22 +1,6 @@
   $ . "$TESTDIR/lib.sh"
-BUG: Fails with no accepted nodes to land.
+Works correctly with no accepted nodes to land.
   $ land
-  hg: parse error: empty query
-  Traceback (most recent call last):
-    File "/Users/kbullock/Source/Projects/hg/accept/tests/../land", line 87, in <module>
-      for r in accepted_ranges(all_accepted):
-    File "/Users/kbullock/Source/Projects/hg/accept/tests/../land", line 53, in accepted_ranges
-      conf.source, accepted_revset)))
-    File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/json/__init__.py", line 290, in load
-      **kw)
-    File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/json/__init__.py", line 338, in loads
-      return _default_decoder.decode(s)
-    File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/json/decoder.py", line 366, in decode
-      obj, end = self.raw_decode(s, idx=_w(s, 0).end())
-    File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/json/decoder.py", line 384, in raw_decode
-      raise ValueError("No JSON object could be decoded")
-  ValueError: No JSON object could be decoded
-  [1]
 
 If only r2 is accepted, nothing happens.
   $ echo `hg log -r 2 -R source --template '{node}'` > bob-accepted