Admin-on-rest : ReferenceInputRequired on create

gistfile1.txt

import {ReferenceInputRequired} from './ReferenceInputRequired';
export const ProductCreate = (props) => (
    <Create {...props}>
        <SimpleForm>
            <TextInput source="name" />
            <ReferenceInputRequired label="Brand" source="brandId" reference="brands">
                    <SelectInput optionText="name"/>
            </ReferenceInputRequired>
        </SimpleForm>
    </Create>
);

ReferenceInputRequired.js

import {ReferenceInput} from 'admin-on-rest';

export class ReferenceInputRequired extends ReferenceInput {
};

ReferenceInputRequired.defaultProps = Object.assign({}, ReferenceInput.defaultProps);
ReferenceInputRequired.defaultProps.allowEmpty = true;
ReferenceInputRequired.defaultProps.validate = (value, _, props) => {
    if (!value) {
        return [props.translate("aor.validation.required")];
    }
};