[feature request] Ability to insert default value in case of missing

[kmonsoor]

In some cases, one of field can be missing as blank. They may have a "de facto" default values, only mentioned when there is an exception.
It would be great, if we could insert default values in case of missing items as like as we are validating an item.
imo, It would greatly pair with "validation" feature.

for example (look at second column):

columns = [
            {'name': 'product_name'},  # Required by default
            {'name': 'product_unit', 'default': 1},
            {'name': 'product_url', 'validator': lambda c: c.startswith('http')}
            # ...
        ]

[santiagobasulto]

Good idea.

[jackunion]

@santiagobasulto if I got everything right, this issue was already fixed, along with a couple of another issues. If it's not a problem, could you close the issues that was already fixed, they are a bit confusing. Thank you.