Integer optional(@Nonnull Integer i) {
        return i == 0 ? null : i;
    }
Convert a non-null Integer instance to a possibly null Integer instance based on ProtoBuf's
rules for optional arguments.

<p>This helper converts an Integer instance from a ProtoBuf object into a possibly null
Integer. In ProtoBuf objects, Integer fields are not nullable, but a zero-value Integer field
is considered to be "missing".

<p>The internal Conductor APIs expect missing arguments to be passed as null values, so this
helper performs such conversion.

@param i an Integer from a ProtoBuf object
@return the original Integer, or null
grpc-server/src/main/java/com/netflix/conductor/grpc/server/service/GRPCHelper.java