Allow first=None for add_implicit_resolver.

git-svn-id: http://svn.pyyaml.org/pyyaml/trunk@155 18f92427-320e-0410-9341-c67f048884a3

1 files changed, 2 insertions, 0 deletions

diff --git a/lib/yaml/resolver.py b/lib/yaml/resolver.py
index 2329c63..7e580e9 100644
--- a/lib/yaml/resolver.py
+++ b/lib/yaml/resolver.py
@@ -25,6 +25,8 @@ class BaseResolver:
     def add_implicit_resolver(cls, tag, regexp, first):
         if not 'yaml_implicit_resolvers' in cls.__dict__:
             cls.yaml_implicit_resolvers = cls.yaml_implicit_resolvers.copy()
+        if first is None:
+            first = [None]
         for ch in first:
             cls.yaml_implicit_resolvers.setdefault(ch, []).append((tag, regexp))
     add_implicit_resolver = classmethod(add_implicit_resolver)