!14 ext_config_image don't need judge wheather be null

Merge pull request !14 from dingwei/master

src/image/image.c

@@ -246,11 +246,6 @@ static struct bim *bim_get(const char *image_type, const char *image_name, const
     }
     if (ext_config_image != NULL) {
         bim->ext_config_image = util_strdup_s(ext_config_image);
-        if (bim->ext_config_image == NULL) {
-            lcrd_append_error_message("Failed to dup external config image %s", bim->ext_config_image);
-            bim_put(bim);
-            return NULL;
-        }
     }
     if (container_id != NULL) {
         bim->container_id = util_strdup_s(container_id);