Get empty string when null

You can use Objects.toString() (standard in Java 7):

Objects.toString(gearBox, "")

Objects.toString(id, "")

From the linked documentation:

public static String toString(Object o, String nullDefault)

Returns the result of calling toString on the first argument if the first argument is not null and returns the second argument otherwise.

Parameters:
o – an object
nullDefault – string to return if the first argument is null

Returns:
the result of calling toString on the first argument if it is not null and the second argument otherwise.

See Also:
toString(Object)