Before this, options with co->data==NULL (i.e. no storage) were not
added to the bridge (except alias options). There are a few options
which might make sense to allow via the bridge ("profile" and
"include"). So allow them.
In command_init(), we merely remove the co->data check, the rest of the
diff is due to switching the if/else branches for convenience.
We also must explicitly error on M_PROPERTY_GET if co->data==NULL. All
other cases check it in some way.
Explicitly exclude options from the property bridge, which would be
added due this, and the result would be pointless.
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