Fix autoinstall-extracting runcmd in the case no user-data is passed.

debian/changelog

@@ -1,3 +1,9 @@
+livecd-rootfs (2.649) UNRELEASED; urgency=medium
+
+  * Fix autoinstall-extracting runcmd in the case no user-data is passed.
+
+ -- Michael Hudson-Doyle <michael.hudson@ubuntu.com>  Thu, 05 Mar 2020 15:35:17 +0100
+
 livecd-rootfs (2.648) focal; urgency=medium
 
   * Enable cloud-init in live server installer live session on all

live-build/ubuntu-server/includes.binary/overlay/etc/cloud/cloud.cfg

@@ -126,6 +126,6 @@ runcmd:
      user_data = yaml.safe_load(subprocess.run([
          "cloud-init", "query", "userdata"],
          check=True, stdout=subprocess.PIPE, encoding='utf-8').stdout)
-     if 'autoinstall' in user_data:
+     if user_data is not None and 'autoinstall' in user_data:
          with open("/autoinstall.yaml", "w") as fp:
              yaml.dump(user_data['autoinstall'], fp)