[FIX] account: on_change_unit_amount do not reset uom to default
[MERGE] forward port of branch 7.0 up to cd31cbf556cc11950ce6188041cf5c2fcd89e0f8
[FIX] account: unit arg of on_change_unit_amount can be False
[MERGE] forward port of branch 7.0 up to 7c5bf67a5f9378fe4ae01eeffff24889f7bdcdc5