Bug 16719: Pass through undef rather than empty string in LDAP mapping

Bug 16719: Pass through undef rather than empty string in LDAP mapping

Nullable DB fields should be passed null in cases where ldap fields are
empty and not replaced with empty strings.

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Joy Nelson <joy@bywatersolutions.com>
(cherry picked from commit 0dac0b874779bc7617490199944af1d2b807e656)

Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>