[#1701] Don't index empty dates as the current one

When parsing an empty string, dateutil will always use a default one,
which by default is now(). We use here a fake date to see if that was
the case, and if so remove the value from the dict to index.

ckan/lib/search/index.py

@@ -3,6 +3,7 @@
 import logging
 import collections
 import json
+import datetime
 from dateutil.parser import parse
 
 import re
@@ -200,11 +201,18 @@ def index_package(self, pkg_dict, defer_commit=False):
         # be needed?  For my data not changing the keys seems to not cause a
         # problem.
         new_dict = {}
+        bogus_date = datetime.datetime(1, 1, 1)
         for key, value in pkg_dict.items():
             key = key.encode('ascii', 'ignore')
             if key.endswith('_date'):
                 try:
-                    value = parse(value).isoformat() + 'Z'
+                    date = parse(value, default=bogus_date)
+                    if date != bogus_date:
+                        value = date.isoformat() + 'Z'
+                    else:
+                        # The date field was empty, so dateutil filled it with
+                        # the default bogus date
+                        value = None
                 except ValueError:
                     continue
             new_dict[key] = value