Set `schema` default in function arg
Set `schema` default in function arg

okfn/datapackage-model-py,datapackages/datapackage-py,datapackages/datapackage-py,sirex/datapackage-py,okfn/datapackage-py,sirex/datapackage-py,okfn/datapackage-py,okfn/datapackage-model-py