Handle corner-case: null reflist.

debian/list.go

@@ -51,6 +51,11 @@ func NewPackageList() *PackageList {
 
 // NewPackageListFromRefList loads packages list from PackageRefList
 func NewPackageListFromRefList(reflist *PackageRefList, collection *PackageCollection) (*PackageList, error) {
+	// empty reflist
+	if reflist == nil {
+		return NewPackageList(), nil
+	}
+
 	result := &PackageList{packages: make(map[string]*Package, reflist.Len())}
 
 	err := reflist.ForEach(func(key []byte) error {

debian/list_test.go

@@ -287,6 +287,10 @@ func (s *PackageListSuite) TestNewPackageListFromRefList(c *C) {
 	c.Assert(err, IsNil)
 	c.Check(list.Len(), Equals, 4)
 	c.Check(list.Add(s.p4), ErrorMatches, "conflict in package.*")
+
+	list, err = NewPackageListFromRefList(nil, coll)
+	c.Assert(err, IsNil)
+	c.Check(list.Len(), Equals, 0)
 }
 
 func (s *PackageListSuite) TestNewPackageRefList(c *C) {