diff --git a/poky/scripts/lib/devtool/upgrade.py b/poky/scripts/lib/devtool/upgrade.py
index ebe7228..0c1de8c 100644
--- a/poky/scripts/lib/devtool/upgrade.py
+++ b/poky/scripts/lib/devtool/upgrade.py
@@ -550,12 +550,12 @@
         try:
             logger.info('Extracting current version source...')
             rev1, srcsubdir1 = standard._extract_source(srctree, False, 'devtool-orig', False, config, basepath, workspace, args.fixed_setup, rd, tinfoil, no_overrides=args.no_overrides)
-            old_licenses = _extract_licenses(srctree, rd.getVar('LIC_FILES_CHKSUM'))
+            old_licenses = _extract_licenses(srctree, (rd.getVar('LIC_FILES_CHKSUM') or ""))
             logger.info('Extracting upgraded version source...')
             rev2, md5, sha256, srcbranch, srcsubdir2 = _extract_new_source(args.version, srctree, args.no_patch,
                                                     args.srcrev, args.srcbranch, args.branch, args.keep_temp,
                                                     tinfoil, rd)
-            new_licenses = _extract_licenses(srctree, rd.getVar('LIC_FILES_CHKSUM'))
+            new_licenses = _extract_licenses(srctree, (rd.getVar('LIC_FILES_CHKSUM') or ""))
             license_diff = _generate_license_diff(old_licenses, new_licenses)
             rf, copied = _create_new_recipe(args.version, md5, sha256, args.srcrev, srcbranch, srcsubdir1, srcsubdir2, config.workspace_path, tinfoil, rd, license_diff, new_licenses, srctree, args.keep_failure)
         except bb.process.CmdError as e: