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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def make_default(spec):
 """Create an empty document that follows spec. Any field with a default will take that value, required or not. Required fields with no default will get a value of None. If your default value does not match your type or otherwise customized Field class, this can create a spec that fails validation."""

    doc = {}
    for key, field in spec.iteritems():
        if field.default is not no_default:
            doc[key] = field.default
    return doc