Fix unmarshaling of nested structs (#340)

Fixes #339

marshal.go

@@ -575,20 +575,22 @@ func (d *Decoder) valueFromTree(mtype reflect.Type, tval *Tree, mval1 *reflect.V
 				}
 
 				found := false
-				for _, key := range keysToTry {
-					exists := tval.Has(key)
-					if !exists {
-						continue
+				if tval != nil {
+					for _, key := range keysToTry {
+						exists := tval.Has(key)
+						if !exists {
+							continue
+						}
+						val := tval.Get(key)
+						fval := mval.Field(i)
+						mvalf, err := d.valueFromToml(mtypef.Type, val, &fval)
+						if err != nil {
+							return mval, formatError(err, tval.GetPosition(key))
+						}
+						mval.Field(i).Set(mvalf)
+						found = true
+						break
 					}
-					val := tval.Get(key)
-					fval := mval.Field(i)
-					mvalf, err := d.valueFromToml(mtypef.Type, val, &fval)
-					if err != nil {
-						return mval, formatError(err, tval.GetPosition(key))
-					}
-					mval.Field(i).Set(mvalf)
-					found = true
-					break
 				}
 
 				if !found && opts.defaultValue != "" {
@@ -626,7 +628,11 @@ func (d *Decoder) valueFromTree(mtype reflect.Type, tval *Tree, mval1 *reflect.V
 
 				// save the old behavior above and try to check structs
 				if !found && opts.defaultValue == "" && mtypef.Type.Kind() == reflect.Struct {
-					v, err := d.valueFromTree(mtypef.Type, tval, nil)
+					tmpTval := tval
+					if !mtypef.Anonymous {
+						tmpTval = nil
+					}
+					v, err := d.valueFromTree(mtypef.Type, tmpTval, nil)
 					if err != nil {
 						return v, err
 					}