AzureSQLMaintenance script doesn't default mode when explicitly passed NULL

[asos-richardevans]

When explicitly passing the @mode parameter as NULL to the AzureSQLMaintenance stored procedure the protection that sets the mode to 'smart' as a default doesn't get executed.

Proposing that the code on line 63 is changed from

if @mode not in ('smart','dummy') set @mode = 'smart'

to

if (@mode not in ('smart','dummy') OR @mode IS NULL) set @mode = 'smart'