round trip nil class

5 files changed, 31 insertions, 3 deletions

diff --git a/lib/psych.rb b/lib/psych.rb
index 3ebc1fa..2d0cf0c 100644
--- a/lib/psych.rb
+++ b/lib/psych.rb
@@ -26,9 +26,23 @@ module Psych
     parse(yaml).to_ruby
   end
 
+  ###
+  # Parse a YAML string.  Returns the first object of a YAML parse tree
   def self.parse yaml
+    yaml_ast(yaml).children.first.children.first
+  end
+
+  ###
+  # Parse a YAML string in +yaml+.  Returns the AST for the YAML parse tree.
+  def self.yaml_ast yaml
     parser = Psych::Parser.new(TreeBuilder.new)
     parser.parse yaml
-    parser.handler.root.children.first.children.first
+    parser.handler.root
+  end
+
+  ###
+  # Dump object +o+ to a YAML string
+  def self.dump o
+    o.to_yaml
   end
 end
diff --git a/lib/psych/ruby.rb b/lib/psych/ruby.rb
index f63fee1..ae007c4 100644
--- a/lib/psych/ruby.rb
+++ b/lib/psych/ruby.rb
@@ -1,4 +1,4 @@
-[Object, String, Class, Hash, Array].each do |klass|
+[Object, String, Class, Hash, Array, NilClass].each do |klass|
   klass.send(:remove_method, :to_yaml)
 end
 
diff --git a/lib/psych/visitors/to_ruby.rb b/lib/psych/visitors/to_ruby.rb
index 8848c16..a37c294 100644
--- a/lib/psych/visitors/to_ruby.rb
+++ b/lib/psych/visitors/to_ruby.rb
@@ -10,7 +10,12 @@ module Psych
 
       visitor_for(Nodes::Scalar) do |o|
         @st[o.anchor] = o.value if o.anchor
-        o.value
+        case o.tag
+        when 'tag:yaml.org,2002:null'
+          nil
+        else
+          o.value
+        end
       end
 
       visitor_for(Nodes::Sequence) do |o|
diff --git a/lib/psych/visitors/yast_builder.rb b/lib/psych/visitors/yast_builder.rb
index 620a2bb..8508601 100644
--- a/lib/psych/visitors/yast_builder.rb
+++ b/lib/psych/visitors/yast_builder.rb
@@ -45,6 +45,10 @@ module Psych
         @stack.pop
       end
 
+      def visit_NilClass o
+        append Nodes::Scalar.new('', nil, 'tag:yaml.org,2002:null', false)
+      end
+
       private
       def append o
         @stack.last.children << o
diff --git a/test/visitors/test_yast_builder.rb b/test/visitors/test_yast_builder.rb
index 3979566..36feb21 100644
--- a/test/visitors/test_yast_builder.rb
+++ b/test/visitors/test_yast_builder.rb
@@ -37,10 +37,15 @@ module Psych
         assert_round_trip(%w{ a b })
       end
 
+      def test_nil
+        assert_round_trip nil
+      end
+
       def assert_round_trip obj
         @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
     end
   end