Fix zipFiler crash on dirs with subdirs

licensedb/filer/filer.go

@@ -323,9 +323,13 @@ func (filer *zipFiler) ReadDir(path string) ([]File, error) {
 	}
 	result := make([]File, 0, len(node.children))
 	for name, child := range node.children {
+	    isDir := true
+	    if child.file != nil {
+	        isDir = child.file.FileInfo().IsDir()
+	    }
 		result = append(result, File{
 			Name:  name,
-			IsDir: child.file.FileInfo().IsDir(),
+			IsDir: isDir,
 		})
 	}
 	return result, nil

licensedb/filer/filer_test.go

@@ -79,9 +79,27 @@ func TestZipFiler(t *testing.T) {
 	filer, err := FromZIP("test_data/local.zip")
 	assert.Nil(t, err)
 	testFiler(t, filer)
+
 	filer, err = FromZIP("test_data/local2.zip")
 	assert.Nil(t, filer)
 	assert.NotNil(t, err)
+
+	filer, err = FromZIP("test_data/empty_sub_dir.zip")
+	assert.Nil(t, err)
+	defer filer.Close()
+	files, err := filer.ReadDir("")
+	assert.Nil(t, err)
+	assert.Len(t, files, 1)
+	assert.Equal(t, "dir", files[0].Name)
+	assert.True(t, files[0].IsDir)
+	files, err = filer.ReadDir("dir")
+	assert.Nil(t, err)
+	assert.Len(t, files, 1)
+	assert.Equal(t, "sub_dir", files[0].Name)
+	assert.True(t, files[0].IsDir)
+	files, err = filer.ReadDir("dir/sub_dir")
+	assert.Nil(t, err)
+	assert.Len(t, files, 0)
 }
 
 func TestNestedFiler(t *testing.T) {