There are two cases that may happen when a user calls Get or GetAll:
1) the attribute is missing
2) the attribute is empty
sss_sifp has two error code to distinguish between those two cases:
1) SSS_SIFP_ATTR_MISSING
2) SSS_SIFP_ATTR_NULL
Usually the caller is not interested on situations when the attribute
is empty and it can be considered as error. Having it as a separate
error code instead of setting the output value to NULL is necesarry
since attribute does not have to be a pointer.
This patch however sets pointer type attributes to NULL since it may
simplify the code path when the caller is actually interested in
this information (e. g. empty server list on domain objects).
It is not possible to send a NULL string over a D-Bus nor it is
possible to have hash table NULL with current code so these two
scenarios are not tested. However, it is handled in sss_sifp_attr
code for completeness.
Reviewed-by: Lukáš Slebodník <lslebodn@redhat.com>