common: Rectify some annotations in NonNullUtils

common: Rectify some annotations in NonNullUtils

In-line genereic type definitions should not have @Nullable/@NonNull
annotations. These should be only on the "real" parameter and/or return
types.

Change-Id: Iba75a9cf6eb9cbe4662eec25089fa91ffa079728
Signed-off-by: Alexandre Montplaisir <alexmonthy@voxpopuli.im>
Reviewed-on: https://git.eclipse.org/r/59324
Reviewed-by: Hudson CI
Reviewed-by: Marc-Andre Laperle <marc-andre.laperle@ericsson.com>
Tested-by: Marc-Andre Laperle <marc-andre.laperle@ericsson.com>