tmf: Bug 416660: -1 long state value is not long

tmf: Bug 416660: -1 long state value is not long

- Do not return nullValue when creating a new int or long with a value
of -1. This ensures that these values can be used and be differentiated
from a null value.

- Change occurences of -1 null value check to use isNull() method.

Change-Id: I7c9e80963736e701a0b30f5f3009a0c7084527bb
Signed-off-by: Patrick Tasse <patrick.tasse@gmail.com>
Reviewed-on: https://git.eclipse.org/r/16396
Reviewed-by: Alexandre Montplaisir <alexmonthy@voxpopuli.im>
IP-Clean: Alexandre Montplaisir <alexmonthy@voxpopuli.im>
Tested-by: Hudson CI