The database value for expiry_date is None for the invite
that will never expire and the clients send -1 as value
in the API similar to the message retention setting.
Also, when passing invite_expire_in_days as an argument
in various functions, invite_expire_in_days is passed as
-1 for "Never expires" option since invite_expire_in_days
is an optional argument in some functions and thus we cannot
pass "None" value.
Sahil Batra