Some might argue that you always need to have a default value and this might be true from a programmer perspective, but from a user perspective this can be quite misleading. All unfilled fields should not be changed on transition to the next task and should only show the placeholder. Here is a list of fields, that are having this unexpected behaviour:

1. listboxes (with the exception of BigInteger & BigDecimal), default value = null.
2. integer and decimal boxes (same exception), default value = 0.