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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 fill_with_defaults(process_input, input_schema):
 """Fill empty optional fields in input with default values."""

    for field_schema, fields, path in iterate_schema(process_input, input_schema):
        if 'default' in field_schema and field_schema['name'] not in fields:
            dict_dot(process_input, path, field_schema['default'])