Make sure we write the kernel config line anyway.

src/modules/grubcfg/main.py

@@ -110,6 +110,7 @@ def modify_grub_default(partitions, root_mount_point, distributor):
                 lines.append("{!s}=\"{!s}\"".format(key, escaped_value))
 
     if not have_kernel_cmd:
+        kernel_cmd = "GRUB_CMDLINE_LINUX_DEFAULT=\"{!s}\"".format(" ".join(kernel_params))
         lines.append(kernel_cmd)
 
     if not have_distributor_line: