BUG-869: added proper handling of nullable parameter

Argument of Function.apply method is marked as Nullable, but previous implementation assumed it
as nonnull parameter.

Change-Id: Ifc49803443d7cc71e7ff7f062f30119840519377
Signed-off-by: Martin Vitez <mvitez@cisco.com>
Merge "BUG-869: added proper handling of nullable parameter"