def validate(self, value):
        if value in self.empty_values and self.required:
            raise ValidationError(self.error_messages['required'])
Initialize nodes structures
dataset/ETHPy150Open wuher/devil/devil/fields/fields.py/DevilField.validate--crossover with--dataset/ETHPy150Open dnlcrl/PyGraphArt/src/graph.py/Graph._init_nodes