3 files changed, 24 insertions, 8 deletions
diff --git a/lib/psych/visitors/to_ruby.rb b/lib/psych/visitors/to_ruby.rb
index 06ab5d1..9b5a253 100644
--- a/lib/psych/visitors/to_ruby.rb
+++ b/lib/psych/visitors/to_ruby.rb
@@ -10,12 +10,15 @@ module Psych
 
       def visit_Psych_Nodes_Scalar o
         @st[o.anchor] = o.value if o.anchor
-        case o.tag
-        when 'tag:yaml.org,2002:null'
-          nil
-        else
-          o.value
+
+        return nil if o.tag == 'tag:yaml.org,2002:null'
+
+        unless o.quoted
+          return nil if o.value =~ /^null$/i
+          return nil if o.value == '~'
         end
+
+        o.value
       end
 
       def visit_Psych_Nodes_Sequence o
diff --git a/lib/psych/visitors/yast_builder.rb b/lib/psych/visitors/yast_builder.rb
index 8508601..90dc8d0 100644
--- a/lib/psych/visitors/yast_builder.rb
+++ b/lib/psych/visitors/yast_builder.rb
@@ -21,7 +21,10 @@ module Psych
       end
 
       def visit_String o
-        @stack.last.children << Nodes::Scalar.new(o)
+        quote = !!(o =~ /^(null|~)$/i)
+
+        scalar = Nodes::Scalar.new(o, nil, nil, !quote, quote)
+        @stack.last.children << scalar
       end
 
       def visit_Class o
diff --git a/test/visitors/test_yast_builder.rb b/test/visitors/test_yast_builder.rb
index 36feb21..30374c1 100644
--- a/test/visitors/test_yast_builder.rb
+++ b/test/visitors/test_yast_builder.rb
@@ -7,6 +7,7 @@ module Psych
       def setup
         @v = Visitors::YASTBuilder.new
       end
+
       def test_scalar
         @v.accept 'foo'
 
@@ -37,13 +38,22 @@ module Psych
         assert_round_trip(%w{ a b })
       end
 
+      # http://yaml.org/type/null.html
       def test_nil
         assert_round_trip nil
+        assert_equal nil, Psych.load('null')
+        assert_equal nil, Psych.load('Null')
+        assert_equal nil, Psych.load('NULL')
+        assert_equal nil, Psych.load('~')
+
+        assert_round_trip 'null'
+        assert_round_trip '~'
       end
 
       def assert_round_trip obj
-        @v.accept(obj)
-        assert_equal(obj, Psych.load(@v.tree.to_yaml))
+        v = Visitors::YASTBuilder.new
+        v.accept(obj)
+        assert_equal(obj, Psych.load(v.tree.to_yaml))
         assert_equal(obj, Psych.load(obj.to_yaml))
         assert_equal(obj, Psych.load(Psych.dump(obj)))
       end