fix: crash with unset source

README.md

@@ -376,7 +376,7 @@ tags:
 - name: Person
   id:
     type: "STRING"
-    concatItems: 0
+    concatItems:
       - "abc"
       - 1
     function: hash

pkg/errors/errors.go

@@ -8,6 +8,7 @@ var (
 	ErrUnsupportedClientVersion  = stderrors.New("unsupported client version")
 	ErrNoAddresses               = stderrors.New("no addresses")
 	ErrInvalidAddress            = stderrors.New("invalid address")
+	ErrUnsetSource               = stderrors.New("unset source")
 	ErrInvalidIndex              = stderrors.New("invalid index")
 	ErrNoSpaceName               = stderrors.New("no space name")
 	ErrNoGraphName               = stderrors.New("no graph name")

pkg/source/source.go

@@ -3,6 +3,8 @@ package source
 
 import (
 	"io"
+
+	"github.com/vesoft-inc/nebula-importer/v4/pkg/errors"
 )
 
 type (
@@ -39,7 +41,8 @@ func New(c *Config) (Source, error) {
 		return newHDFSSource(c), nil
 	case c.GCS != nil:
 		return newGCSSource(c), nil
-	default:
+	case c.Local != nil:
 		return newLocalSource(c), nil
 	}
+	return nil, errors.ErrUnsetSource
 }

pkg/source/source_test.go

@@ -3,9 +3,18 @@ package source
 import (
 	. "github.com/onsi/ginkgo/v2"
 	. "github.com/onsi/gomega"
+	"github.com/vesoft-inc/nebula-importer/v4/pkg/errors"
 )
 
 var _ = Describe("Source", func() {
+	It("ErrNoSource", func() {
+		c := Config{}
+		s, err := New(&c)
+		Expect(err).To(HaveOccurred())
+		Expect(err).To(Equal(errors.ErrUnsetSource))
+		Expect(s).To(BeNil())
+	})
+
 	It("S3", func() {
 		c := Config{
 			S3: &S3Config{