don't error if no source image id was not passed

packer/registry/image/image.go

@@ -50,10 +50,6 @@ func (i *Image) Validate() error {
 		return errors.New("error registry image does not contain a valid ProviderName")
 	}
 
-	if i.SourceImageID == "" {
-		return errors.New("error registry image does not contain a valid SourceImageID")
-	}
-
 	return nil
 }
 
@@ -70,7 +66,6 @@ func (i *Image) String() string {
 // calling f(k,v). The func f is responsible for type asserting the expected type for the key and value before
 // trying to create an Image from it.
 func FromMappedData(mappedData interface{}, f func(key, value interface{}) (*Image, error)) ([]*Image, error) {
-
 	mapValue := reflect.ValueOf(mappedData)
 	if mapValue.Kind() != reflect.Map {
 		return nil, errors.New("error the incoming mappedData does not appear to be a map; found type to be" + mapValue.Kind().String())