Comment 1 for bug 1841697

Thanks for filing a bug.

I can recreate this using your config file. It appears to be related to the shell parsing of that value, if you leave a space before the start of the list and the end like so:

diff -u /etc/cloud/cloud.cfg.d/90_dpkg.cfg.bad /etc/cloud/cloud.cfg.d/90_dpkg.cfg
--- /etc/cloud/cloud.cfg.d/90_dpkg.cfg.bad 2019-08-28 01:28:14.064394783 +0000
+++ /etc/cloud/cloud.cfg.d/90_dpkg.cfg 2019-08-28 01:26:12.279439013 +0000
@@ -1,2 +1,2 @@
 # to update this file, run dpkg-reconfigure cloud-init
-datasource_list: [ConfigDrive, None]
+datasource_list: [ ConfigDrive, None ]

I believe this is due to manual modification of the file, correct?