Better unmarshalling for "null".

Fixes #35.

decode.go

diff --git a/decode.go b/decode.go
index 1a87da9..5f00702 100644
--- a/decode.go
+++ b/decode.go
@@ -288,6 +288,14 @@
 	return good
 }
 
+var zeroValue reflect.Value
+
+func resetMap(out reflect.Value) {
+	for _, k := range out.MapKeys() {
+		out.SetMapIndex(k, zeroValue)
+	}
+}
+
 var durationType = reflect.TypeOf(time.Duration(0))
 
 func (d *decoder) scalar(n *node, out reflect.Value) (good bool) {
@@ -302,6 +310,15 @@
 	if set := d.setter(tag, &out, &good); set != nil {
 		defer set()
 	}
+	if resolved == nil {
+		if out.Kind() == reflect.Map && !out.CanAddr() {
+			resetMap(out)
+		} else {
+			out.Set(reflect.Zero(out.Type()))
+		}
+		good = true
+		return
+	}
 	switch out.Kind() {
 	case reflect.String:
 		if resolved != nil {
@@ -378,17 +395,11 @@
 			good = true
 		}
 	case reflect.Ptr:
-		switch resolved.(type) {
-		case nil:
-			out.Set(reflect.Zero(out.Type()))
+		if out.Type().Elem() == reflect.TypeOf(resolved) {
+			elem := reflect.New(out.Type().Elem())
+			elem.Elem().Set(reflect.ValueOf(resolved))
+			out.Set(elem)
 			good = true
-		default:
-			if out.Type().Elem() == reflect.TypeOf(resolved) {
-				elem := reflect.New(out.Type().Elem())
-				elem.Elem().Set(reflect.ValueOf(resolved))
-				out.Set(elem)
-				good = true
-			}
 		}
 	}
 	return good

decode_test.go

diff --git a/decode_test.go b/decode_test.go
index 46c94d4..7042908 100644
--- a/decode_test.go
+++ b/decode_test.go
@@ -316,7 +316,10 @@
 		map[string]*string{"foo": new(string)},
 	}, {
 		"foo: null",
-		map[string]string{},
+		map[string]string{"foo": ""},
+	}, {
+		"foo: null",
+		map[string]interface{}{"foo": nil},
 	},
 
 	// Ignored field
@@ -372,7 +375,7 @@
 		map[string]time.Duration{"a": 3 * time.Second},
 	},
 
-	// Issue #24. 
+	// Issue #24.
 	{
 		"a: <foo>",
 		map[string]string{"a": "<foo>"},
@@ -630,6 +633,30 @@
 	}
 }
 
+var unmarshalNullTests = []func() interface{}{
+	func() interface{} { var v interface{}; v = "v"; return &v },
+	func() interface{} { var s = "s"; return &s },
+	func() interface{} { var s = "s"; sptr := &s; return &sptr },
+	func() interface{} { var i = 1; return &i },
+	func() interface{} { var i = 1; iptr := &i; return &iptr },
+	func() interface{} { m := map[string]int{"s": 1}; return &m },
+	func() interface{} { m := map[string]int{"s": 1}; return m },
+}
+
+func (s *S) TestUnmarshalNull(c *C) {
+	for _, test := range unmarshalNullTests {
+		item := test()
+		zero := reflect.Zero(reflect.TypeOf(item).Elem()).Interface()
+		err := yaml.Unmarshal([]byte("null"), item)
+		c.Assert(err, IsNil)
+		if reflect.TypeOf(item).Kind() == reflect.Map {
+			c.Assert(reflect.ValueOf(item).Interface(), DeepEquals, reflect.MakeMap(reflect.TypeOf(item)).Interface())
+		} else {
+			c.Assert(reflect.ValueOf(item).Elem().Interface(), DeepEquals, zero)
+		}
+	}
+}
+
 //var data []byte
 //func init() {
 //	var err error

yaml.go

diff --git a/yaml.go b/yaml.go
index 6370416..903b13b 100644
--- a/yaml.go
+++ b/yaml.go
@@ -88,7 +88,11 @@
 	defer p.destroy()
 	node := p.parse()
 	if node != nil {
-		d.unmarshal(node, reflect.ValueOf(out))
+		v := reflect.ValueOf(out)
+		if v.Kind() == reflect.Ptr && !v.IsNil() {
+			v = v.Elem()
+		}
+		d.unmarshal(node, v)
 	}
 	return nil
 }